"When you see me wave this flag, use your right hand and pull down on the strap that has the red ribbon."

I listened dubiously to the matter-of-fact instructions given by the black-skinned, muscular Mexican in bathing trunks, one of a five-man crew handling the parachute ride on the beach at the Holiday Inn here.

They had just strapped me into a life vest and harness. Behind me on the sand, a big, multicolored chute flapped and fluttered nervously as if eager to taste the wind. Competent, business-like but willing to talk, these young Acapulcanos said they liked the Americans because they were relaxed, fun-loving and willing to take a chance.

I had just signed a release form that said I absolved everybody (except me) of any responsibility for what I was about to do. I had already paid them 150 pesos ($6.80). And I was about to let them attach a rope to the harness, a rope that trailed along the beach, ran into the bay and up onto a speedboat. In a minute the man in that boat would get a signal to gun his engine. Then I was supposed to fly.

fly? Dios mio! This gringo was definitely not relaxed. But it was too late to back out.

What offers unexpected vacation encounters, a tingling but not-too-dangerous taste of adventure, a pleasant cross-cultural experience, and a colorful, amusing, sun-splashed bilingual show?

Give yourself 80 points if you answered: "The Parachute ride that carries tourists 25 to 30 stories above the beach and Acapulco Bay."

You score a full 100 if you said "Acapulco."

Signs of clamorous, inexorable growth assault the startled eyes and ears of one who has returned after an eight-year absence and who had visited the city more than once 10 years before then. No longer languorous, it literally explodes along the crowded Costera Miguel Aleman - though, to be sure, there are still pockets of lazy, tropical sanity away from town. Regretfully, the place no longer rates high on my personal list of vacation hideaways. But, of course, vacations are a very individual matter; it depends upon what you are looking for.

The coast of the Mexican State of Guerrero, about 250 miles south of Mexico City, continues to draw hordes of sun-loving North Americans and other foreigners with its combination of dependably warm temperatures year-round, miles of beaches facing one of the world's most attractive harbors, excellent hotels, good food, plenty of activities both day and night, good buys in native crafts and fine quality silver, and that unique not-to-be-underestimated-in-importance brand of friendly smiles and service.

Yet, it's true that Acapulco has many faces, not all of them attractive or happy. We'll look at some of them. And I am also well aware of certain incidents in the recent past involving Mexican politics and a spate of crimes (mostly drug-related and occuring in another state) than badly hurt the tourism business and caused our Latin neighbor to suffer severe economic losses for a time.

But, fortunately, that period is over. Business is booming, deservedly so. Mexicana Airlines has just reported that it carried 51 percent more U.S. passengers last January than in January 1977, a year in which the airline set records. An official candidly credited the country's improved political and economic climate, along with better scheduling - so the Mexicans themselves have not forgotten.

In talking to visitors, it quickly becomes obvious that there is one critical word that perhaps gives the best clue to why they have chosen to vacation in Mexico: "Friendly."

Travel industry officials around the world don't need to be reminded that they are in a highly competitive business. Almost every country, large and small, has entered the race, seeking to tempt ever-increasing numbers of foreign-exchange-bearing vacationers - though there are serious doubts in some quarters about the benefits of tourism and its proper role in the Third World.

Everyone wants a piece of the so-called discretionary dollar (however maligned and sagging on the international markets lately), the pound, the Deutchmark, yen, franc, etc. Even that anticapitalist revoluntary Fidel Castro.

During my stay here, members of Mexico's industria sin chimeneas (industry without chimneys) - hotel representatives, airline officials, operators of ground transportation - met with package wholesalers and tour operators from a number of countries to talk developments and mutual problems, and to plan tour packages that will later sold to the public through travel agents, airlines and other retail outlets.

These professionals are familiar with the lure ofMexico's sun - first worshipped with bloddy offerings by the country's ancient Indian civilizations, whose incredible ruins and artifacts draw millions of sightseers, and now deified again by affluent winter-weary moderns who sacrifice only their money. Mexico knows how to market its beaches, its culture, its creative accomplishments, its excitement.

But it also recognizes that its real treasure, its trump card in the tourist game, is the warmth of the Mexican people, whose pride and firm grasp on their national and individual identities allow them to greet visitors with genuine friendliness rather than with out-stretched palms. This was again clearly evident to me.

Yet, unfortunately, the Mexicans are no strangers to deprivation and poverty, and while the poor are not easily seen in antiseptic, somewhat artificial Cancun, that beautiful and expensive resort built from scratch a few years ago off the Yucatan coast, they are quite visible in Acapulco.

Acapulco has, after all, been around for decades. The sights, sounds and smells are for real.

The boat leaped forward across the windswept bay, and the rope attached to my waist pulled me across the sand. Airborne! In seconds I was floating higher than the highest hotel on that curving stretch of beach. Below me sparkled the bay and not far away surged the Pacific.

It was long way down. Relax, I told myself. After all, what could go wrong? Well, the rope could break, letting me drift over the scrubby, rain-starved hills that ring the bay or smash into one of the beachfront hotels. Or the harness or chute could come loose, dropping me into the deep in a longer dive than those daredevil Mexicans make daily at La Quebrada. And I can't swim.

I was glad the crew told me they inspect all the equipment every few months. I hoped nobody had been cutting corners - or cutting anything, for that matter.

There was absolute silence and very little sensation while hanging from the chute. The view was worth the price. Now the boat was turning and we were heading back to the hotel. There one was the man with the flag. He dropped it, so I didn't have to do anything. (One woman had ignored the signal as I watched earlier, and had come close to hitting the hotel at the 20th-floor level before the competent skipper zoomed seaward again and brought her down safely on the beach. A few riders had wound up in the water. One plopped atop a pile of clothes being sold in a open-air, thatched-roof bazaar.

I landed gently on the sand. The flight had lasted only a couple of minutes. Another "performer" immediately took off to the amusement of hotel guests enjoying the day-long show while sunning. The same scene was being repeated at a number of other nearby beach areas, where similiar crews work on commission for the same employer. Though this is a more advanced part of the Third World, the daily battle fought by many natives still involves earning just barely enough to buy food and pay for simple shelter. (Fortunately, the climate in Acapulco minimizes the need for clothing and elimates any expenditure for heating.) Just about anywhere you go here, somebody will try to sell you something.

On the beach, along the sidewalk, and even in the middle of the street while cars stop for a traffic light, vendors of all ages offer their wares. Their Indian heritage is readily apparent. An elderly, brown-skinned man in a broad-brimmed sombrero waits patiently all morning near the parachute crew with small plastics replicas of the chute and rider, the hat man and the basket man stroll by with a load of their products, a woman displays sailing ship models of wood. Others try to sell dresses and jewelry (the summer crowd is not as free with its cash as the winter season groups), a youth kneels on the sand and upwraps strips of bark decorated with colorful designs, little children give impromptu rhythmic performances for bathers, and a small, slender boy walks the beach all day carrying a box of Chiclets to bring home a few pesos to a widowed mother.

At the Plaza de Artesanias, too, the Indian side of Mexico is very apparent as vendors hail tourists in English and try to entice them over to their stands, where many good buys in Mexican-made crafts can be found, particularly colorful pottery. Bargaining is definitely the rule - for example, a large decorated straw bag may be priced to begin with at 700 pesos, but a little good-natural haggling may bring the final price down to 80 pesos.

But unless a visitor has seen the same item elsewhere and knows he is being asked to pay an exorbitant sum (in many regular shops the price is firm and there's no bargaining), he should not play the hard-driving, pinchpenny role. There's nothing wrong with seeking a fair bargain, but it's not such an accomplishment to cut deeply into the small earnings of somewhat at the poverty level.

However, in buying silver or gold jewelry some caution is indicated. In the case of a few inexpensive trinkets for gifts or personal use, there's no reason not to look over the wares offered on the street, in the markets or on the beach. But be wary of what seems to be a real "steal," because you can't b sure what carat that gold item represents or whether the silver is actually plated or a mixture of other metals. Good Mexican silver is beautiful, priced right, and free of U.S. Customs duty if it would be valued at more than $18 per dozen. So buy your silver and gold at reliable silver shops to avoid a costly awakening. And always check prices and compare - unless you're a Texas millionaire.

The increase in ambulatory vendors and the frenetic resemblance to bad aspects of some crowded U.S. cities are the natural results of the high Mexican birthrate, which continues to compund the country's problems of growing poverty, inflation, lack of jobs and inadequate arable land. The population explosion poses a major threat to sincere, Herculean efforts by President Jose Lopez Portillo to maintain political and economic stability and build confidence in Mexico's future.

There is cynicism among some Mexicans about whether the wealth expected fron the nation's vast oil reserves will filter down to the lower classes. And tepid government efforts at birth control must contend with the Mexican love of large families, machismo, religion and the simple belief that "cada hijo trae su pan abajo subrazo" (each child brings his bread under his arm). Just as is the case in Mexico City, though on a much smaller scale, impoverished Indians leave their villages and descend upon Acapulco in the hope of finding food and work. For any thinking American who loves Mexico or just loves to vacation there, these matters are relevant to the tourism experience - and how the resulting flood of illegal immigrants in the United States is dealt with eventually could affect attitudes on both sides of the border.

For the American bearing battered dollars, the news here today is far brighter than in Europe. As a result of devaluation, the peso is now worth only about 4 cents U.S (which, of course, is bad news for the Mexican seeking to buy U.S. goods or travel abroad). At a bank the rate of exchange is about 22.50 pesos to the dollar, though your hotel and the shops will probably give a flat 22 pesos.

Which means that though the government has permitted hotel rates and food prices to rise slightly, and thus this tends to offset somewhat the benefit of devaluation for foreigners, Mexico still remains a best vacation buy - except for the high air fair which has not yet been brought into line with reduced transcontinental and transatlantic bargains fares. An ocean-view double at the Holiday Inn resort (don't turn up your nose - there's little resemblance to the standard roadside inn) costs about $30. A buffet breakfast, with juice (not fresh), delicious fresh papaya, watermelon and pineapple, eggs, beans, sausages, ham, tortillas, coffee or milk runs about $3.40. Or pay more a la carte for eggs to order, toast, steak, etc.

Don't count on the bank at the modern Acapulco Airport to be open. It's not much of a dependable convenience and was closed when I arrived from Dulles via Dallas on a direct Braniff 727 flight (I miss the faster, gas-guzzling 707). So it's a good idea to buy a small packet of pesos before leaving the United States to use for initial tips (10 pesos to the airport porter for a normal-sized suitcase; handing out dollar bill is more expensive). Incidentally, a bellboy should recieve 10-20 pesos, depending on the service, and a maid about 10 pesos a day. Tip 15 percent at restaurants (don't try to convert, figure the tip on the local pesos sum).

And unless you travel alone, don't fall for the smooth pitch in English by the concessionaire as your limo (no cabs permitted to pickup at the terminal) pulls out the airport, gate. Pay him for the one-way trip to town ($3 per person) but don't buy the return voucher. If there are three or four people in your group, it will be cheaper to return by cab. Be sure you save 100 pesos ($4.50) to pay your departure tax, an airport fee charged by many countries that I have always considered to be an insulting farewell to the tourist who has already dropped a bundle.

Clothes present no problem. Just about anything goes in Acapulo. As "Guide Magazine," the complimentary publication edited by Sloane Simpson, points out: "Men never need wear either ties or jackets unless they are planning on being married or buried." No socks either. Shorts, jeans or slacks are fine. Bathing suits will get you almost anywhere by day if you wear some kind of cover-up.

Health conditions are quite good. Six months ago, the government opened a new water purification plant located many miles from Acapulco. Water from a distant river is now treated and piped into this city, which has long suffered from a water shortage. At times of scarcity, tourists in luxury hotels along the beaches would enjoy their showers while residents in many less-fortunate areas would have no water. Now there is no cause for guilt feelings, and the sign posted in many room at the Holiday Inn clearly states that the tap water is safe to drink, a major improvement over the past.

However, if you think you like to be doubly careful (even the mere change of water from one U.S. state to another can trigger an intestinal upset), order sealed bottles of the excellent Mexican mineral water - "sin gas," without carbonation. Most important, don't buy food from street vendors, do not eat uncooked vegetables or fresh salads (one of the foremost experts on Moctezuma's Revenge, Dehli Belly, etc., warns that the only way to sterilize a head of lettuce in countries that may irrigate with contaminted water or use human waste as fertilizer, is "with a blowtorch."), and don't munch any fresh fruit you can't peel. Meat should be well done. The milk and dairy products served in major hotels are safe.

While some beaches are quite crowded and thus less appealing that I like, the government is continuing studies of conditions in the bay and maintains there are no pollution hazards. According to the Acapulco News, the government has decided to move the naval base from Acapulco to Michoacan, possibly because the real estate - prime oceanfront - is needed for more hotels and facilities to serve even more visitors. There have also been recurring reports of contaminattion caused by naval vessels, which is denied by military authorities. Fears of pollution are also cited in connection with a suggestion that the government oil facilities in the same area should also be moved.

My quarrel with the beaches along a major section of the hotel strip involves hazards caused by undertow, sharp dropoff, crosscurrents and wave action rather than cleanliness. Not only is there danger for small children, who should be watched carefully, but even good adult swimmers should exercise caution.

What do you do when you're tired of the beach and shopping?

Take a day or moonlight cruise on the bay; sign up for a day or night tour of the city, or pick an excursion to Zihuatanejo, Ixtapa, Taxco or Mexico City if you have extra days to spare. Watch a bullfight (Sundays only), provided you don't think the "sport" is cruel; see those high divers at La Quebrada, or visit the Centro Acapulco, which is now a combined cultural and convention center offering a restaurant, bars, ballet, cinema, theater, variety shows and a disco.

Speaking of discos, for many young visitors the disco scene is really where it's at. They start dancing at 11:30 p.m. and are still gyrating at 4 or 5 a.m. They then recharge their batteries on the beach for the next night.

Arriving tourists who respect Mexico's laws are rarely hassled by customs and immigration personnel at this port. Most suitcases are never opened, since Mexico genuinely wants to give a warm bienvenida to all visitors.

Last month in Mexico City, the United States signed what was described as its "first diplomatic agreement dealing exclusively with tourism." Fabian Chavez, assistant secretary of commerce for tourism, who heads the United States Travel Service, called it "a milestone in promotion tourism and international relations." The agreement is supposed to "facilitate tourism traffic between the two nations. . . ."

I hope that means my welcome by the Dallas contigent of U.S. Customs will be smoother upon this return than the last time, when one conscientious agent sifted methodically through everything my wife and I carried back. I couldn't blame him, though. My wife had purchased a clay cooking pot in Mexico City that trip. At New Orleans the smiling agent asked automatically, "what have we got?" My wife answered honestly, "Just a little pot."

We almost missed the plane to Washington.