SHIP AHOY! It's a white sales season for bargain-hunting cruise Guffs.

Increased cabin capacity during a tight economy means a soft market and hardball competition, resulting in stepped-up passenger discounts from now through summer by almost every cruise line. (Ask specific lines, or your travel agent, about cutoff dates.)

"Fly-free" packages are proliferating and have spread from the Caribbean to some Alaska and trans-Canal cruises. Offers of airfare "add-ons" are also continuing, though they have not always been as much of a savings as touted. Some lines even provide complimentary land packages.

You can forget about booking far in advance. According to Joseph Paige, senior vice president, marketing, for Miami's Norwegian Caribbean Lines and chairman of the marketing committee for CLIA (Cruise Lines International Association), no one bothers to book six months in advance these days.

"People are booking closer and closer to the actual sailing time," said Paige. "The economy is the main reason. They want to hold onto their money and who can blame them. But that's what hurts the industry and further softens the market. A soft market, however, does benefit a customer since ships have to be filled."

Paige pointed out that anyone who does book in advance does not lose out on any later discounts or promotions offered. Every line--at least the 28 members of CLIA--guarantee the reduced-rate airfare add-ons and special gimmicks and prices in effect at the time of sailing. The lines will attempt to make it up to the advance buyer, although Paige did not say how.

He also mentioned that in the last 90 days the cruise business has shown more strength than at the same time last year, indicating the market is slowly regaining its health.

How will that affect your being able to find a bargain cruise? Not very much yet, said Paige. He explained that new ships entering service this year and next will further increase the number of beds to be filled while the cruise industry confronts a sagging economy and stiff competition. That means good news for buyers.

When you shop for your bargain cruise, consider the shorter ones, like the three- and four-day trips to the Bahamas or the week-long Caribbean sailings where competition is so keen that you're bound to do well. An extra bonus this season is that the special offers are being extended to Alaskan and trans-Canal sailings and to the transatlantic crossings of Cunard's QE2.

"You will get value for your cruise," Paige promised. "The special promotional efforts of cruise lines do not mean you will get a real cheapie trip, but you will receive one of value at a good price and considerably lower than any other vacation."

Main departure ports continue to be Miami (the leader), Fort Lauderdale (Port Everglades), San Juan, New York and West Coast cities.

Two new ships on the horizon: Carnival's Tropicale, already in service out of Miami but switching to the West Coast in May, and Home Lines' Atlantic, scheduled to begin weekly cruises to Bermuda from New York on April 17.

If you're thinking of booking on a brand-new ship, Paige recommends that you wait a while. The new ones are always booked solid anyway--the exception to the current rule. After several sailings, this usually tapers off.

Following is a partial listing of cruise line offerings:

Carnival Cruise Lines: They claim the lowest rates in the seven-day cruise market and continue to guarantee all rates for 1982 regardless of how far in advance you book. The guarantee applies also to the airfare add-ons. The line's "Super C Saver" price (on a space available basis for bookings within 30 days of sailing) is being continued indefinitely. The Fly Aweigh air add-on for the Washington area is $140 per person, added to the cost of the cruise.

Costa Cruises: Now, through Dec. 11, it's fly free or pay a $100 add-on for passengers on World Renaissance seven-day Caribbean cruises. Starting April 17, the same deal will apply to the Carla C and the Daphne, all sailing out of San Juan. Here's how this one works: You get the free airfare if you book an outside cabin on any of the ships. You pay $100 for roundtrip air tickets from this area to Puerto Rico, plus your cruise fare, if you book an inside cabin.

Cruise rates for the World Renaissance start from $775; the Carla C from $795, and the Daphne, $895--all per person, double occupancy.

For the line's Bahama cruises on the Amerikanis, there's a complimentary two-night hotel stay at either Orlando, Port Everglades or Miami Beach. That vessel sails out of Port Everglades.

Cunard Line: The business traveler with meetings in Europe who travels transatlantic on the Queen Elizabeth 2 can take his spouse along for free. You must book and pay for a single outside stateroom and one-way British Airways economy ticket to or from London. In return, you'll get an outside stateroom for two and two air tickets. BUT, you must complete all travel within 12 days, and that includes the five-day crossing on the ship. This limited offer begins April 17, continues through December, and is available in either transatlantic direction. Confirmations are required 60 days before sailing. There are also hotel discounts in London.

Additionally the cruise line is offering free airfare to or from Europe for all QE2 passengers on all 24 transatlantic trips. You can also fly British Airways directly from Washington to London, returning by ship to New York, and you will be entitled to an allowance of $500. The line's hotels, land tour and cruise combinations are also being discounted.

Cunard has also announced that all youths between 12 and 26who cross the Atlantic on the QE2 without their parents during the April-December season,will pay only $445 on a shared cabin basis. Port taxes are an additional $45. A non-motorized bike can be brought along without charge. "Applications will be honored on a stand-by basis with confirmation usually made one month prior to sailing," according to Cunard.

Regular transatlantic fare ranges from $1,095 to $5,725 per person, double occupancy. Three crossings will be made from Philadelphia to help that city celebrate its 300th birthday.

Eastern Cruise Lines: Like Costa, this line is also offering free land stays with a choice of areas in connection with Emerald Seas' four-day Bahamas cruises. To qualify you pay full fare, based on two to a cabin. The land stay also includes free car rental and free admission to some attractions. You have to book cabin categories I-6, and the offer is valid through Aug. 30 (except May 31 and July 5).

Third and fourth passengers in the same stateroom with two full fares cruise for free, but the land portion is not free for them.

Holland America Cruises: If you like Bermuda and New York, the line will pay your roundtrip airfare to New York (or in some cases charge you only $25 as add-on) to sail on either the Veendam or Volendam, which move from Miami to the Port of New York in April. There's also a 10 percent discount on all Spring Caribbean cruises on the Rotterdam out of New York.

Next fall, the line will be sailing from new Florida ports with the Volendam and Rotterdam using Port Everglades and the Veendam out of Tampa. The Port of Miami is building two more new passenger terminals that will not be completed in time to accommodate HAC ships. Also, the port prefers to give priority to ships based there year-round, and several new ones will be added this fall.

Home Lines Cruises: To celebrate the line's new ship, the Atlantic, sailing from New York, April 17-Oct. 16, third and fourth persons in a cabin--regardless of age--will only pay 50 percent of the minimum fare.

Norwegian Caribbean Lines: Their Cloud-9 fly/cruise programs charge $100 for air add-on using Air Florida and $135 when the carrier is Pan Am, in addition to the cruise fare, April-September.

Royal Caribbean Cruise Line: There's an air add-on of only $50 for this area on weekly cruises out of Miami and free airfare on their 10, 11 and 14-day air/sea packages.

Sitmar Cruises:This line has gone all out in expanding its fly/free feature to all passengers by offering free roundtrip airfare to East and West Coast embarkation ports for all cruises to the Caribbean, Mexico, Canada/Alaska and trans-Panama Canal. Free airfare is applicable to even third and fourth persons, regardless of age, and in all of the line's 15 different cabin categories.

William T. Kyle, senior vice president, marketing and sales, feels that the line's cruises are "especially attractive to vacationers who want the most value for their limited discretionary income."

He indicated that stopover privileges with the air/sea programs cost very little or nothing, depending upon selection. Details are available from the line.

There are many more discounts and offers, all worth investigating. Don't drag your anchor.