HAVE YOU, too, wondered if a cruise ship is really a good place to spend a vacation? Without having tried it, I had decided that it wasn't. With all the carefully cultivated snobbery of the small-boat sailor who looks on anything powered by a motor (except as an auxiliary to wind) as a "stink-pot," I thought that a cruise ship was a big, fancy stink-pot populated by little old ladies in tennis shoes.

I am not quite sure what it was that overcame these misconceptions and persuaded me to cruise the Caribbean under power. Perhaps it was a handsome, multicolored brochure from Sun Lines advertising a "cruise ship with a yacht itinerary" - a cruise, that is, which stopped at small islands and out-of-the-way ports. Perhaps my sailors prejudices were not really as deep-seated as I thought. You can, after all, enjoy a decent shower and sleep in a comfortable bed on a cruise ship, while many a yacht bunk is about as roomy as a coffin.

Whatever the explanation, I recently spent two surprisingly pleasant weeks on the Stella Oceanis, a small (6,000-ton) liner owned by the Marriott Hotel chain but run by Greek shipping magnate Charalambos Alex Keusseoglou with a Greek registration and crew. We cruised from San Juan, Puerto Rico, to Ciudad Guayana on the Orinoco River in Venezuela and back, stopping as advertised at tiny Caribbean islands such as St. Eustatius, the Isles des Saintes and Bequia, as well as some of the more familiar spots such as Barbados, Antigua, St. Lucia and Tobago.

As a cure for unreasoning prejudices, this was a first-rate prescription. Still, there are both pluses and minuses to be recorded in any assessment of cruising. Other skeptics may be interested in balancing them.

The biggest plus is variety: 14 different islands in 14 days. There is, if anything, too much variety. The Caribbean begins to become a kaleidoscopic blur; if it's Sunday, it must be Guadaloupe.You yearn to stop for two or three days and really get to know an island - Barbados, for example, or Grenada or St. Lucia. Mart Rickey, the stand-up comic on board our ship, puts it this way:

"You think you're seeing a lot of islands, but you're not. We're sailing round and round the same island. Each time we dock, they put up a different sign."

Some people use a cruise as a sampling device - to find "their" island and then go back to stay longer. Within limits, this is a sound idea, though it is hard to get a real feel for an island in a day, much less a few hours.

Still, if you tried to sample the Caribbean by any other method, it could not be done in anything like 14 days. Even if you could get to all the islands by plane (you can't) and count on never being bumped from a flight - which you certainly can't in the West Indies - you would spend so much time packing, unpacking, checking, checking out, reconfirming reservations, taking cabs to and from the airport that there would be scarcely any time left. On a cruise, your hotel room goes wherever you go.

This is an especially big plus for inexperienced travelers and people of retirement age who dislike the hassle of conventional travel. There is no doubt that a cruise ship is convenient. It can also be a little like home, if you are lucky, in that you get to know the passengers, the waiters, the chief steward, the cruise director, the hostesses and the entertainers - and sometimes the captain, if he is personable and gregarious, as Stavros Dandouras, our captain, was.

There is also organized activity, if you consider that a plus. Sometimes it is. I learned to skeet-shoot, for example, in time taken somewhat reluctantly from bikini-watching at the pool. I skipped the calisthenics, the lectures on avoiding tax liability, the organized bridge, the Greek lessons and most of the movies.

You need to do some homework, in advance, on the islands you will be visiting. It is too late, once you dock, to begin wondering what you ought to see and do; and neither shipboard orientations nor organized shore excursions are wholly dependable.

If you know where you want to go at each port, you can promptly hire a cab to take you there. Share the cab with friends and it won't be expensive. The Caribbean Tourist Assn., 20 East 46th St., New York, N. Y. 10017, will provide information and maps, as will the governments and tourist bureaus of the several islands. One good plan is to identify and visit one or two of the best resort hotels. Most are glad to grant you free use of their beach and pool for a day - they figure (rightly) that you will be buying food and drink.

The biggest disadvantage of cruising is the price. It will cost you between $150 and $300 a day, double, and while that is not a great deal more than some of the best resort hotels (transportation and food are included on a cruise) it is still steep. Not many cruises are for low-and middle-income people, though sometimes people will save for years to be able to take a sea trip.

You need to consider the crowd. Many of the longer cruises (10 days to two weeks) attract primarily the older set; the under-40 group, with less time and money to spare, usually chooses seven days or less. Moreover, young people tend to take vacations in the summer, while retired people can get away at any time. The only way to be sure of a congenial crowd is to travel with a nucleus of friends - five or six, if you can, the size of an assigned dinner table.

Some miscellaneous suggestions:

Come early to the port of embarkation. Don't wait until the day you sail and then fly down from the north. Particularly in winter, there can be delays, missed connections, canceled flights. Moreover, Old San Juan, the 450-year-old, once-fortified Spanish town at the entrance to San Juan harbor, is itself well worth a day or more. A good hotel is El Convento ($65-$70 double), a restored 17th-century Carmelite convent with a picturesque and highly photogenic courtyard.

Bring binoculars. You will need them on the ship, and on land, almost constantly.

You may want to pack formal wear (check with your travel agent or the cruise line in advance to determine policy). Some cruise ships remain one of the last refuges of the tuxedo and evening gown. If formal wear is often posted, you'll want to dress up. Otherwise, you will feel quite comfortable in more casual attire (though bathing suits are usually frowned upon at meals except at poolside).

Wear tennis shoes, because you'll do a lot of walking - unless you shuttle primarily between deck chair and dining room.

Never take a wallet ashore. Or a watch. The purser's office has safety deposit boxes. Carry your money separately - money you can afford to lose - but not credit cards and personal papers. Sometimes there are changing rooms and lockers at the beach but no often, and it can be unsafe to leave valuables unattended. Even aboard a ship.

Don't turn up your nose at the cabins on the lower decks just because they used to be called "second class." Except for a few luxury cabins, all the outside ones are about the same size, regardless of deck. The lower you are, and the closer to amidships you are, the less you feel the motion of the boat. Inside cabins (without portholes) are less desirable.

Get acquainted, early and pleasantly, with the chief steward. He is one of the most important people on board for your comfort and convenience. If he is on your side, much will go smoothly.

Be flexible; don't complain about trifles. You may not like being herded here and there like poor little lambs who may go astray. You may chafe at being required to eat dinner at an exact time (15 minutes' leeway) or when told you must explore an island in only four hours. But there are reasons for most of these requirements, and complainers are soon ostracized. A cruise ship is a close, gossipy small town.

The things that are good are often very good indeed. The food on this vessel, except at breakfast, was superb. And some of the entertainment was fine - we enjoyed a "Greek night" with dance and costume, and a "Caribbean night" with an excellent steel band and native dancers.

The positives almost certainly will out-weigh the negatives. Even a small-boat sailor risks being converted. And if he actually admits he has enjoyed being on a "stink-pot," you can be sure someone has been doing something right.