A colleague mentioned the other day that he and his wife had been thinking about taking their first cruise. But, he confessed, "we don't know the first thing about how to choose the right one for us." It's not surprising the couple is confused. As many as 150 cruise ships sail the world's seas, and no two are exactly alike. You can pick a compatible ship and have a great vacation, or sail on a bummer and rue the day you wasted so much money.

Price, of course, is a major factor, but it should not be the only basis for reaching a decision. The ship's style, itinerary and size are also important considerations. Carnival Cruise Lines calls its growing fleet "the fun ships," and its brochures depict a youngish bikini-clad crowd in frenzied activity. Society Expeditions' clientele appears older; photos in its brochures might show them with binoculars and boots studying penguins in the Antarctic.

Depending on your personal tastes, you can select from among ships that:

Promise a lively nonstop party, or fill your evenings with scholarly lectures.

Dock at a new port every day, or rarely go near a port.

Seek out sun-drenched beaches, or explore ancient cities and other historical sites.

Feature budget-conscious three- and four-day getaways, or cruise leisurely on itineraries that stretch on for weeks and months.

Cater to families -- Premier Cruise Lines identifies itself as "the official cruise line of Walt Disney World" -- or make themselves available to such special-interest outings as cruises for nudists only, singles only or gays only.

If you prefer intimacy, it can be found on small ships, such as those operated by the American Canadian Caribbean Line, which carry as few as 76 passengers. But as might be expected, on-board recreational facilities are, by necessity, very limited.

On the other hand, Royal Caribbean Cruise Line's new Sovereign of the Seas, the largest liner afloat, is a full-fledged resort in everything but name -- offering practically everything except 18 holes of golf. It can carry more than 2,200 passengers: When the Sovereign docks at a Caribbean port such as St. Thomas in the Virgin Islands, passengers spill into the streets like an invading army.

On my first cruise a few years back, aboard Norwegian Cruise Line's Sunward II, a magnificent sunset rewarded our last night at sea. The sky was so spectacular, the captain made an announcement over the public address system urging everyone to go on deck and take a look. Hardly anybody showed up, however, and my wife and I continued to watch in pleasant solitude. Later we discovered why: Our fellow passengers were engrossed in bingo. If there were ever a next time, I told myself, I would find a ship catering to folks who prefer scenery over games.

"There are different breeds of travelers," says Ron Bitting, president of the National Association of Cruise Only Agencies. "You've got the backpackers," by which he means adventurous travelers, "and you've got the traveler who needs to plan a year ahead and wants to know what side of the bed the phone is on." Despite this variation, he says, "there is something for everyone in cruising."

Bitting's organization represents about 800 travel agencies nationwide, including those that handle nothing but cruise vacations as well as full-service agencies with separate cruise divisions. The goal of the specialists is to match passengers with a cruise they will enjoy -- which, despite the romantic ballyhoo of cruise line advertising, is no easy matter.

A travel agent himself for almost three decades, Bitting heads Personal Touch Cruise Consultants of Freeport, N.Y. He has put together a detailed questionnaire, which his staff uses to determine the interests of his customers. Among the very specific questions: Do you prefer a new ship sleekly modern in decor or an older one that reflects an earlier era? If you like an older ship, he suggests sailing the 30-year-old Rotterdam of Holland America Line. "It's so beautifully maintained."

One tip to getting a ship you will like, says Bitting, is to find one that offers activities similar to those you enjoy on land-based vacations. If you tell Bitting you want to sample several beaches, he probably will book you on a ship plying the Caribbean. If gambling, disco dancing and a vibrant night life are most important to you, he will find you a party ship. In the first example, itinerary is of primary importance, he notes; to the night owl, the ship's activities come first, regardless of its destination.

Among the major considerations when choosing a cruise vacation:

Price: "In all instances, price is important," says Bitting. "Everybody is price conscious. We have people booking $20,000 cruises, but they want it for $19,500."

Last-minute bargains often are available, because many new ships have been built recently and the availability of cabins has outstripped demand -- at least temporarily. But Bitting cautions that the bargains are not for everyone. You don't, for example, get first choice on cabins and often have to take the leftovers.

An easy-going traveler -- the backpacker, says Bitting -- may have no difficulty adjusting to whatever ship is offering the best price currently. But those people who demand certainty "are fooling themselves if they think they can take advantage of these offers." Their choices are limited, and they will not like it. "It's an emotional thing."

Generally, the more you pay for a cruise the classier the ship you get. Service should be more attentive, and your cabin should be larger and better located. At the top of the scale, you can book a two-room suite with a private verandah open to the sea. For this, you might pay as much as $2,000 a night for two people.

The cheapest cabins may have no window or porthole and be located in the ship's equivalent of the basement. For real savings, four adults can share a bunk-bed cabin at a rate of perhaps $125 to $150 a day per person. Some travel counselers suggest these tight, remote quarters shouldn't matter because you spend very little time in your cabin. If you are claustrophobic, however, you probably will be happier with an outside cabin, and the closer to open air the better.

The major cruise lines -- that is, those with fleets of large ships offering a variety of activities -- can be loosely grouped in price categories. Bitting lists the following among the lower-priced, mass-market lines: Chandris Fantasy Cruises, Celebrity Cruises, Norwegian Cruise Line, Carnival Cruise Lines and Royal Caribbean Cruise Line. In the mid-price range, he puts Holland America Line, Princess Cruises and Royal Cruise Line. Upper-scale cruise lines are Royal Viking Line, Cunard Line and Crystal Cruises.

Among the specialty cruise lines with upscale cabin rates are those that provide a luxury yachtlike experience. These include Seabourn Cruise Line; Renaissance Cruises, which has introduced the all-suite concept to the sea; the Club Med 1, a five-masted motorized sailing vessel cruising less-visited islands in the Mediterranean and Caribbean; and Windstar Sail Cruises.

Also upscale but in a category of their own, says Bitting, are the expedition or adventure cruise lines, whose ship-board and off-ship activities are strongly educational in content. These lines include Society Expeditions, Salen Lindblad Cruising and Special Expeditions.

Obviously, longer cruises are more expensive. But many travelers don't have the money or the time for lengthy vacations at sea. In line with an industry trend toward shorter cruises, Society Expeditions next year is introducing its version of the short cruise: a series of itineraries designed to fit within a two-week time frame, including travel time. Most of the line's itineraries are 15 to 29 days. The cost of the line's shorter cruises is expected to be less than $300 a day per person, based on double occupancy.

Destination: Cruise fans will tell you a cruise is the best way to tour foreign lands, because you always have a comfortable cabin waiting at the end of the day and you have to unpack only once. This, of course, should be taken with a grain of salt. A day in port is hardly time enough for anyone to get to know a city or country. At the very least, a port call is an introduction to a destination that may lure you back on your own at a later date.

Cruise itineraries tend to fall into three major categories: recreational, cultural and educational.

The primary recreational destination for Americans is the Caribbean, both for its sunny beaches and shopping ports such as San Juan and St. Thomas. If your goal is fun in the sun, opt for a Caribbean cruise. When in port you can, of course, skip the beaches and the boutiques for a quick personal or escorted tour of island villages, historical sites and scenic attractions.

For a deeper cultural experience, the most popular itineraries are the ancient ports of the Mediterranean Sea as well as Scandinavia, the west coast of Mexico, the islands of Hawaii, the South Pacific and South America. Such cruises schedule frequent sightseeing excursions, providing you with a glimpse of local life.

Into the solidly educational category fall cruises that highlight wildlife viewing or the study of remote and exotic lands. Invariably, one or more guest lecturers are on board to offer evening briefings -- perhaps the night's entertainment -- and to accompany off-ship excursions. These destinations include the Inside Passage to Alaska, which has wildlife, historic and scenic appeal; the Arctic and Antarctica; the Amazon River; and the islands of Indonesia and the Indian Ocean.

Style: On my first cruise, the ship's communications system broadcast light rock music from morning until night. I am not a fan of this kind of music, but there was almost no escaping it. The sound filtered into our room from the hallway speakers just outside the door. The experience taught me a lesson. If you choose to cruise, do so on a vessel that is not going to assault your sensibilities.

For many travelers, style can be at least as important as price.

Style can mean such simple differences between ships as whether dinner seating is in one or two shifts. Typically, seating aboard ships with two shifts is at 6:15 and 8:15 p.m. If you are dining early, you can expect to be hurried along by a staff that has to clean up and set the tables again for the late seating. On a single-seating ship, more time usually is available for a leisurely meal. Royal Viking Line makes a big point of advertising single seating on its ship the Royal Viking Star.

Or style can reflect more fundamental differences in a cruise experience. As Bitting points out, the large, mass-market ships -- such as those in Carnival's "fun" fleet, which sails year-round on a variety of Caribbean itineraries -- offer Las Vegas-style shows, discos, boutiques, health spas and gambling casinos. They appeal to gregarious, often younger travelers on a limited budget who are looking for a good time. If you favor the bustling activity of a big resort hotel, you probably will get along fine on a large cruise ship.

No matter what cruise style you choose, it's important to keep in mind that the cost of all activities is included in the price you pay. A basic seven-day Carnival cruise -- including air fare -- ranges from about $1,000 to $2,100 per person, depending on cabin choice. And although even this price may seem hefty, it includes almost everything: food, lodging, recreation, entertainment and, in many cases, round-trip air fare.

However, if you don't expect to take advantage of the activities -- if, for example, you have little interest in lavish entertainment or casinos -- you may want to consider a different style of cruise, perhaps opting for a ship where your money buys instead a fancier cabin or a longer cruise. On the Sunward II, I was never able to stay awake for the midnight buffet, nor was I much interested in the extra calories.

Presumably there is fun to be had on the cruises offered by adventure lines such as Society Expeditions. But don't expect a lot of revelry. More sedate enjoyment comes in the form of scholarly pursuits, such as joining in on a full-day trek in southern Madagascar to view the famous ring-tailed lemurs in the Berenty Reserve, an option on Society Expeditions' 20-day cruise of the Indian Ocean, which departs Capetown, South Africa, on March 26.

Yet another entirely different style of cruising is available aboard the little 76-passenger Shoreham II, operated by American Canadian Caribbean Line. The vessel's shallow draft permits it to sail right up to remote beaches where a ramp in the bow can be lowered to disembark passengers. Passengers can swim and snorkel without the crowds of a huge ship or a popular resort beach.

Beginning in November, the New Shoreham II will cruise the Bahamas and the Caribbean retracing the voyages of Christopher Columbus, who touched on some islands that still remain well off normal cruise paths. The captain, a student of Columbus lore, will provide a daily commentary. The 12-day voyages, commemorating Columbus's discovery of the New World five centuries ago, begin at $1,190 per person; air fare is additional.

If you are considering a cruise for the first time:

Be aware of what you are looking for in a cruise experience. Sort out your priorities.

Ask friends and relatives who have sailed for recommendations.

Consider checking one of the standard guides to cruising available in bookstores, such as the "Berlitz Complete Guide to Cruising" by Douglas Ward ($13.95). The book provides a numerical evaluation of 125 cruise ships based on such characteristics as cleanliness, cuisine, passenger space, service, activities, shore excursions and decor.

Consult a travel agency experienced in cruise vacations. Most cruises are sold through travel agents. A list of local cruise-only travel agencies can be obtained by sending a stamped, self-addressed envelope to the National Association of Cruise Only Agencies, P.O. Box 7209, Freeport, N.Y. 11520. Specify no more than three states. For information: (516) 378-8006.