IT IS NICE to know as you leave the open area in old Jerusalem where the mosques of Islam are and start to enter the narrow little stone streets leading to the Via Dolorosa, that if you hear somebody above you shout, "Hey, lady!" or "Hey, man!" and you look you you will see some little Palestinian kids up, there on the little balcony and roofs, and they will spit down upon your innocent upturned face. Don't look up and do wear an old hat. Guidebooks don't tell you great stuff like this. In guidebooks you'll find a rare mention of which way to go around the world by ship. Most sane world cruises keep heading west and to give proper credit to Columbus, eventually get back to where they started. The British seem to like to go the other way. Nobody understands this, least of all the British. It is the wrong way to go. I will tell you why.

To do so, I will have to explain the International Date Line. This is something you seldom find in a guidebook. A day has to start somewhere. So you stretch an imaginary trip wire from pole to pole out there in mid-Pacific where it is not going to be a big inconvenience to the locals. Going west, no matter when you trip over the wire, you fall into the next day. Three-fifteen in the morning Tuesday becomes 3:15 in the morning Wednesday. Twenty-four hours are gone in a twinkling. And how are they made up? During the 80 days of the trip, an extra hour here, an extra hour there, it averages 20 minutes a day of extra rest.

When the QE2 trips over the wire going the other way, it falls backward from say, a Saturday to a Friday, making an eight day week with two Fridays. So to get back on track, they have to get rid of the extra 24-hours by taking a wee bit off the whole voyage, an hour here, an hour there. Back in the home port the weary travelers come fumbling off the ship, gray and shaken, whipped for sleep, along with the surly crew members who have come to believe their voyage endless.

That's why Nathan Hale said, "Go West, old man."

There is theory that nations that were once very very successful in a certain endeavor, eventually wind up being worse at it than any other nation. Some obvious examples are: the Italian army, Greek art, American know-how and British seamanship.

It is reputed that Cunard stirred up the fuss between Argentina and the Falklands because after too many eastwardly voyages, they couldn't fill the QE2 any other way.

Take along your little phrase books and take a shot at the language everywhere you go, except China and France. The Chinese and the French don't care to have you trying to speak their language. Both of those civilizations think they are placed at the exact center of the known universe, and foreigners had best stick to their own barbaric gabblings and not sully the finest language in the world by trying to speak it, no matter how fluently.

A pretty Chinese woman in Mexico explained to me why, when I had been stationed in China some years ago, they had absolutely refused to understand my phonetic Mandarin.

She frowned, trying to think how to put it, then her expression cleared and she said, "It would not be wise to understand your dog if he asked you for a meat loaf, would it?" And then she realized what she had said and blushed. A pretty Chinese woman blushing is even prettier than before.

The great shame of the United States citizenry is the large number of us who go to Mexico and make absolutely no attempt to speak the simple phrases of courtesy. (Buenos dias. Gracias. Como esta? Muy bien. Adios.)

Of all the people in the world, the Mexicans seem to me to be the ones most anxious to be tolerant of someone stumbling along in their language. Never laughing, as we so often do at the foreigners trying to speak English, they are eager to help. It is their country, and making no attempt at all is gross and rude.

I remember being in a small Mexican supermercado and a tourist man was in there -- purple pants, blue sneakers, yellow shirt and a fresh green palm-frond hat. Evidently he couldn't find something he wanted, and he started yelling: "Dozen no one speak English in this dump? Dozen no one speak English?"

I was of no mood to help him and hoped the Mexicans present took me for a German. But one tall elderly man in wrinkled seersucker went over to him and said: "Yes. Someone here does speak English. One person, and it certainly is not you, you vulgar little twit." And with enormous dignity, the Englishman left.

We have driven all over Mexico, getting along well enough with all our pidgin Spanish, wherein all the verbs are in the present tense: I go yesterday. I go tomorrow. Etc. We have broken down on rural little roads to nowhere and have received far more courteous help than we could have expected north of the Rio Grande.

It is the way to see the country and the people. We buy bread and wine and cheese in little towns, and picnic in the hills. The Mexicans are fabulous instinctive mechanics. One need only look at the age of the buses that still lumber through the countryside.

Reservations en route are a real problem in Mexico. In the winter holiday season, no Mexican travel agent can help you. The hotel keepers know they will fill up anyway, so why pay a portion of the overnight fee to a travel agent?

Even in the busiest season you need no reservations if you follow one simple rule of the road: Arrive before 5 p.m. There will always be a room because a Mexican family on vacation will keep going as long as there is a scrap of daylight.

You can check in before 5 p.m., unpack, have a couple of nourishing hits of tequila and go into an empty dining room at 7 p.m. After a leisurely meal, when you come out of the dining room, you will find the lobby jammed with luggage, irate and indignant people banging on the front desk, children crawling around the tile floor and harried clerks trying to keep from sending two parties to the same room. All is confusion, and you have eluded it.

Hotels in such places as Veracruz, Tampico, Villahermosa and Merida -- just like the hotels in the bigger cities -- prefer credit cards to cash, and they run the card through the machine and make you sign the blank charge slip before you get your room key. This takes many [Americanos] aback. They think they are going to be cheated.

But at the end of your stay you are shown the total charges. If you want to pay cash rather than use your card, it is fine with them. They will give you all copies of the charge slip you signed and you can tear them up. It is their protection against people who would walk out without paying.

When we had a working burglar alarm system on one of our vans, one that we twice drove to Yucatan from Florida, we used the alarm system all the way through the states down to the border, setting it every night in the motel parking lots. As soon as we were well across the border, we stopped using it.

Years ago we drove all the way down to Cuernavaca towing a little Jeep trailer full of household goods. Anybody could have gotten into it at night by slashing the canvas or untying the ropes. Nobody tried.

I am not saying, Mexico is a totally safe place. Just that it is safer than most -- if one can keep from roaming the barrios of Mexico City at 3 in the morning, or if one can refrain from going into a cantina, waving a roll of bills and demanding romance. I am merely saying that more Mexicans I have met are kind and honorable than in any equivalent sampling of my peer group.

But, as with most people of the Western world, their character changes when they drive. Some of the bridges are not wide enough for two cars. In the daytime, the first driver to put his lights on has the right of way. I do not know what they do at night because I do not drive in Mexico at night. In spite of much legislation, there are still too many farm animals wandering loose, too many holes in the roads big enough to hide a bison and too many peasants full to the brim with tequila, zigzagging back and forth across the shoulder.

And beware, in the oil districts, the huge tank trucks and pipe trucks. The drivers of those big rigs have some strange variety of machismo. Keep an eye on the rear-view mirror because they will blow by you at such speed, hitting the air horns as they pass, that startled gringos have been known to jump their Buicks right into the ditch.

It is not wise or useful to join big tour groups of Americans going to Mexico. The big diesel buses go 90 miles an hour whenever the road is reasonably straight. The hotels they take you to are damned well tired of Americans, and the service and food are at best mediocre. But, worst of all, you are taken to some of the most fascinating ruins in the hemisphere at those hours when they are most crowded, the tour buses standing in dusty formations as far as the eye can see.

For great Mayan ruins such as Palenque, Coba and Chichen Itza it is best to drive to the little Hotel de las Ruinas you will find at each site. They are either owned or operated by Club Mediterranee, and they are smart, clean and cheerful, with a pool and good enough food. Then you can get up in the morning and walk the ruins as soon as the ticket booths are open.

Unless you enjoy grotesque fiction, do not employ a guide. Their inventiveness is exceeded only by their ignorance of Indian history. Too bad because often the truth is more startling than what they invent.

At Chichen, for example, they will show you a circular hole about 60 yards in diameter with the water level beginning about 50 feet below ground level. The sides are sheer. The guide will tell you solemnly that they used to throw the virgins in there as sacrifices to the gods. The archeologists will tell you that they would toss a little kid in there, 9 or 10 or 11 years old, and if he was still alive the next morning, they would fish him out, and he would then have the talent to predict the weather for the next growing season.

In the early morning, the shades and legends and the bloody victims are almost tangible around the pyramids. In a windless silence your footsteps are loud in an unseemly way. Stone faces grimace at you. They were a tough people. They weren't supposed to know about the wheel. But they left carvings on their walls of cog wheels, large and small, the cogs intermeshed. And they chiseled out a huge-stone roller in Coba and used it to roll and flatten the limestone road they built for scores of miles through the jungle, from Coba to Chichen Itza.

Acapulco is Mexico in the same way as Miami is Florida. You can stretch out in your suite and watch old "Bonanza" episodes on television with Hoss Cartwright speaking perfect Spanish. You can rent a suite that has a pink Jeep and a private pool that goes with it and will find stationery in the desk with your name imprinted on it when you arrive. And you will come upon some of the top-tier drug dealers who have come down from Miami to spend some of the bread they have made off the Colombianos.

We're back at sea now, where it is notice to know how best to adjust to those shipboard captain's receptions and champagne parties. Where there are three and four and five and six hundred people aboard, the poor captain is supposed to smile and nod and shake hands with every one of them, and stand there looking noble and captainly and unbored. On a long cruise, like a world cruise, because lots of people take segments of the cruise, you are going to run into a lot of those parties.

On most ships they happen in a huge ballroom or lounge or place where they put on the entertainment -- a lively, overamplified, short-cut performance of "Oklahoma!" or "State Fair" or "South Pacific," with members of the cruise staff filling out the casts of thousands.

People come early and stand in line so they can be greeted early by the captain and they can go in, find the kind of seats they want and start slugging down the freebies. Because they stand there in their finery forming a very long line that usually goes up a couple of flights of stairs, the ship saloons are empty. So the way to handle it is to estimate how long the line will last.

If the reception and free drinks start at 6:30 p.m., and there are 400 people aboard, you can send out a spy at 7 o'clock to take a look at the line. If it is down to about 40 couples, then you can finish your drinks in the quiet comfort of the bar, stroll down, be greeted, go out another door and return to the saloon. Otherwise you will have to sit with a batch of bombed-out strangers and wait too long for your freebie. It is easier and better and more civilized to buy your own. Drinks are not all that pricey aboard the ships.

Should you be invited to eat at the captain's table, you might take a shot at it -- if it is a very short cruise. On a long cruise it is boring and fattening. You can't leave until the latest arrival has finished his gummy dessert. At least half the people at the table will have some sort of hearing problem. One will tell the same three incidents over and over at a meal. And you will have to take your turn buying wine for the whole table.

IT IS NICE to know that there is but one correct direction when you walk around the around the deck. Counterclockwise, please. On the old English ships that used to make the long run from Southampton to Australia loaded with young people emigrating, the decks were so narrow and the passengers so lively they had to post a notice saying: "It is customary to walk counterclockwise. You may go in the opposite direction if you choose, but you will create endless annoyance."

The notice was correct. There will always be a covey of fat ladies going clockwise, and you will always meet them in the narrowest part of the transit, and they will always glower, wondering why all you people are going the wrong way.

To avoid pointless conversation while walking your 20 turns around the deck of a morning, wear a Sony Walkman. You need not turn it on. It is enough to appear as though it were turned on.

You will notice one irrational aspect of deck-walking. On blowy days, when the ship corkscrews along with a slightly sickening motion, there are no barriers. But come a marvelous day with the sun high and the sea sparkling, the deck hands will come out and rope off the whole bow and start slopping paint about, and they are in no great hurry to get the job done. All ships topside look strange if examined closely. This comes from thousands of hours of languid painters, enjoying the sunshine and whacking paint on top of paint until, in some cases, the fittings under 40 thick coats are practically invisible.

Housekeeping topsides and in the common rooms is never remarkably good. Friends traveled on a renowned ship for almost two weeks. Every morning the first one up would go and look out into the corridor where, in a corner, there was a small pile of debris topped by half a breakfast roll.

"Still there!" the earlier riser would announce.

And, indeed, it was still there when they disembarked. They said goodbye to it.

A note of warning. If you are a cigar smoker of the type who refuses to go out onto the open deck, who prefers the common rooms, the dining room, the lounges -- and who is always lighting up when the ship is rolling -- there is now a group of vigilantes who police the cruise ships of the world, grasping cigar smokers by night and hefting them over the rail into the dark sea below. Oddly enough, nobody has ever reported them missing; so the pastime is apparently without risk.

IT IS NICE TO KNOW that when you travel, even after preparing yourself for a special place by reading everything you can find, you will still be astonished.

The first time we took a ship through the Panama Canal, I was astonished to find the countryside between the two big groups of locks so beautfil. You cruise Gatun Lake for hours, past tropic islands, jungled slopes, flights of bright birds. In season, the small-heavy showers bounce silver rain off the decks. All the literature speaks of tremendous engineering feats, yellow fever, the Gaillard cut, the mechanical mules that pull the ships through the locks. They leave out the beauty of the natural scenery.

The guidebooks delight in telling you that in crossing from the Atlantic to the Pacific you travel in a southwesterly direction. I do not find that sufficiently mind-boggling to elicit awe.

We went through the Suez Canal recently. I had read up on it, but I was not prepared for the reality, for the gigantic holding area in Suez Bay where they divide the waiting ships into convoys, with small special convoys for hazardous materials.

I was not prepared for the weathered little sign in front of the administration building at El Suweis, which said in English: "Welcome to the Suez Canal. Have a nice day."

I was not prepared for the utter flatness of 103 miles of sand, the long straight shots into the distance, the lines of the banks meeting at infinity. I did not expect to see a littler of war debris -- shattered vehicles, tanks, trucks, unidentifiable junk -- spread across sandy wastes. I did not expect to see an apartment building on the west bank of the canal, shattered long ago by Israel artillery and air attack.

I did not expect to see Egyptian soldiers manning gun emplacements on that west wide, aimed east, over our heads. There were a lot of ratty little boats about and ragged workmen, digging at the banks in such a desultory fashion it was difficult to imagine what they were tyring to accomplish.

Most of all I was unprepared to have some Egyptian army jokers set off a huge charge in the desert in midafternoon over on the east side, off our stern quarter, about 200 yards away. It made an enormous CRACK-BLAM! and sest up a black mushroom cloud about 200 feet in the air. Four hundred tourists leaped into the air at that moment, some from a supine position near the pool. Two hundred and eleven drinks were spilled. And a whole swarm of Egyptians on the bank started whooping and jumping about and waving and laughing so hard some of them were rolling on the ground.

This was the first and last example of Egyptian humor I have ever seen. They seem to be a hard-luck folk. The Aswan Dam rendered their canal water so stagnant that it developed organisms that give the farm workers and poor folk debilitating intestinal parasites.

IT IS NICE to know that you should not go into the Cairo Museum and give a friendly guard a paper dollar for the four quarters he displays on his wide brown palm. Through an exhibition of perfect sleight-of-hand, he will take the dollar and hand you the stacked coins, with one quarter on top of three other Egyptian coins of the same size but worth a cent-and-a-half apiece. Hard luck encourages ingenuity.

As a matter of fact, you would be sane to skip the Cairo Museum entirely. Three factors militate against enjoyment. It is a dark place illuminated by 40-watt bulbs, and very few of those. At least 17 generations of children and hungry adults have fingered the outside of the glass cases while eating stickies and wet meat pies. And the guides use amplifiers to make themselves heard by their little groups, so that at any given time you can be in a small dim sweaty room with your guide yelling electronically at you in English over the din of other guides yelling the same stuff simultaneously in French, German, Spanish, Egyptian, Hindi, Japanese and anything else you can think of.

But you may wish to visit the museum for exactly those reasons. After all, if you come back home and Uncle Ed asks you what Cairo was like, if you had a beautiful and rewarding and uneventful tour of the marvels of dynasties long gone, you have absolutely nothing to tell Uncle Ed.But if you saw a ragged pedestrian scraped off the side of a bus, and if you had a room on the 8th floor of a hotel where the elevators didn't work, the air conditioning didn't work and there was no way to get a fan or get the window open, and there were nine of you at dinner and all but one came down with food poisoning and that one wasn't you, and then you went to the Cairo Museum . . . Get the picture? Come home with a catalogue of disasters and you can make a lively conversation. Come home with a collection of beautiful slides and you might as well go around ringing a little bell and moaning.

I probably shouldn't be writing about travel because when all is said and done, I am not a very ardent tourist. A little way into my trip, I can get all cathedraled out, museumed to a finish, galleried empty and shopped down to a nub.

IT IS NICE to know that long cruises and world cruises tend to set up shuttle buses running on schedule to take you from dockside to the center of the city. These are very useful in Singapore, perhaps the cleanest large city in the world, where taxis are very scarce in the huge port area and on return trips, like to drop you way out at the gate, a mile and a half from home and mother. Shuttle buses in Bombay generally drop you in the area of the Taj Mahal Hotel where, off a corridor between the old and new parts of the hotel, you can find a splendid Chinese restaurant called the Golden Dragon, where you can be served spiced dishes from Human and Szechwan that will make tears roll down the cheeks of the unwary.

This is a good place to say something about eating ashore while on cruises. Many people think it's a gross extravagance to eat ashore inasmuch as you are already paying for the meal aboard. On some of the Russian cruise ships, I have heard, it becomes a necessity to eat ashore whenever possible, to ward off the debility of slow starvation. A happy balance is recommended.

In Papeete, for example, if there is time to rent a car and circle the larger island of Tahiti (do not try to take that little road that goes around Tahiti) you can find shoreside semi-French restaurants that will serve you a veritable washtub (child size) of mussels in their shells cooked in garlic and butter. Or in the late afternoon you can take a cab up to one of the two decent restaurants high in the hills (reservations please) and have drinks and dinner and watch the Pacific dusk settle over the large harbor of Papeete way way below you. The food is average, but the view and the ambience will stay with you from then on.

If you are on a ship that frequently visits a port you know nothing about, it is best to forget the guidebooks and recommendations for gourmets and simply ask some of the permanent staff people aboard about good places to eat.Not Americanized places -- because you get that on the ship. But places where the locals eat and the food is indigenous and good. That is the way we found a place in Madeira, halfway up the hills, where we ate on a rooftop near a charcoal grill where a man cooked our giant "sardines" -- each as big as a keeper brook trout -- and we ate cheese and hot breat and drank delicious dollar-a-bottle wine while enjoying the midday view.

Stay away from famous eating places! Very very few in this world have been able to handle fame. For instance, Raffles Hotel in Singapore will provide you with one of the most memorably bad and overpriced meals you can find anywhere and will charge you $6.20 for two small glasses of weak beer. The beer, however, is better than the famous Singapore Sling which, as served at Raffles, seems to be orange Kool-aid with a slight rum flavor. In Singapore there is a Chinese restaunt on the 5th floor of the great Mandarin Hotel which, though pricey, serves incredibly good food with flair and style. If the restaurant itself should become famous, I am certain it will begin to decline to the dreary level of Ruby Foo's in Mahattan.

Sometimes the tourist trap-dinner combination is something you should not miss. For instance, it would be almost criminal not to take one of the dinner boats around Hong Kong harbor at night. Once upon a time a wise Englishman named G. K. Chesterton visited New York and stood in Times Square at night and remarked how truly beautiful it would all be if one could not read. It you cannot read Chinese, the harbor scenes in nighttime Hong Kong are fabulous indeed.

While giving this topic a glancing blow, let us return to Mexico for a moment and discuss what you should eat as well as where.

When Jimmy Carter lapsed into truly shoking taste and tried to make a jolly joke out of Montezuma's revenge (also known as the Aztec two-step) he was memorializing the idiocy of the traveling American whose idea of playing it safe is to go to a huge deluxe hotel for lunch and order a chicken salad sandwich.

A lot of the distress is due to the water -- not the water itself but the change of water. People who have lived comfortably abroad for years have been startled to come home and, within a few days, find themselves with, say, a Cleveland version of Montezuma's revenge.

But certain precautions are in order. Do not drop your guard in Mexico merely because you are eating at a big and famous hotel. Their kitchen habits are no cleaner than they would be at a roadside restaurant. Drink beer and wine and Coke and club soda. Eat the indigenous cooked dishes -- tortillas, quesadillas, tacos, refritos, enchilades and so on. If you are from the Southwest, you will find Mexican cooking not as chili-hot as you are used to. Avoid salads. Stick with fruit you can peel.

If you have a compulsion to play Mexican roulette, you can snack from the sidewalk hot-carts. As far as places to sit down and eat, your best sources of information is from Americans living in Mexico -- not the retireds who live in little enclaves of controlled terror and eat exactly what they always eat at home in Binghampton, but the Americans who work there. They are not hard to find in the cities. There are lots of them. And lots of fabulous places to eat.

Never travel without Lomotil, the tourist's best friend. Tiny white tablets, a prescription antispasmodic that will still the churning gut and silence the cramps with a miraculous efficiency. A good prescription antibiotic for tummy trouble is sulfaguanadine. it doesn't work its magic until it is in the intestinal tract.

A final note I crib from a paperback now on the stands titled "Nothing Can Go Wrong" written by me and Capt. John Kilpack (Fawcett/Crest, 394 pp., $3.50). What do cruising and Mexico have in common? They are both very soothing to the sort of person I am. I am a workaholic with an addiction to sloth. Aboard a ship in transit I find that I can take a nap without guilt because I am not really doing nothing. I am traveling. A one-hour-nap carries me 20 miles into my uncertain future. In Mexico, of course, a nap is compulsory. It is called a siesta.

Copyright (c) 1983, John D. MacDonald Publishing Inc.