Sing a song about islands, Mon, sing a song of the sea. Let's sing a song about islands, Mon, that's where I wanna be!

THE LURE OF the sea and the islands this fall and winter could prove to be irresistible with cruise lines offering new itineraries, discounts and even free round-trip flights to ports of embarkation.

Many lines have increased their prices from 6 percent to 15 percent over last season because of higher operating costs. But they are still subsidizing a portion of their cruise packages in a highly competitive market at a time of increased stateroom capacity, economic concerns and continued consumer belt-tightening.

For travelers more nervous about family finances than the air traffic controllers' strike, attractive add-on air fare rates for Washington/Baltimore-area departures are very good news indeed.

Cruise lines understandably want to fill those thousands of ship beds.

New ports appearing on cruise itineraries include St. Croix, Antigua and the Mexican Caribbean. The changes are primarily in direct response to repeated passenger surveys. Some are for economic reasons. Although not one cruise line would admit it when questioned, a few island ports are being dropped because of political factors (instability, anti-American rhetoric, etc.).

Some shiplines are allowing for more hours at sea and less time in port for two good reasons. Passengers -- especially veteran cruise fans -- enjoy the high seas and often remain on board when the ship docks, while the lines save on fuel and maintenance costs (fewer stops and starts conserve oil).

It is evident from surveying the cruise lines that they all anticipate another soft winter travel season in the Caribbean, which means that unless they offer some attractive enticements they, too, could suffer along with island hotels and economies dependent on tourism. Rather than up anchor with too many empty cabins, they'd rather take a small cut in profits and sail away with a full ship. The thinking is that once lured aboard a vessel, the first-time passenger will return again when economic indicators are healthier.

Interestingly enough, the lines queried also revealed that cruise passengers now often can book as late as three weeks prior to sailing time. In past seasons, bookings had to be made three to six months in advance to guarantee availability of space. Of course, even today a late booking may not get you your first choice in accommodations.

Here's what some cruise lines are offering:

Bahama Cruise Line, New York City, will put the Veracruz into weekly service Oct. 24, sailing from Tampa, Fla., to Mexico's Caribbean ports of Cancun and Cozumel plus a stop at Florida's Key West. These continue through May 8, 1982. Cruise prices start from $545. The line offers air/sea add-on rates of $195 for round-trip flights from the Washington-Baltimore area. For another $195 they feature a seven-day optional land stay in the Yucatan.

Although this ship sailed to Caribbean ports out of St. Croix last season, it did experiment with a Tampa-to-Mexico trip. And that's how it came to change the entire fall/winter program this season.

Carnival Cruises Lines, Miami: "Never assume that a ship is sailing full," is the word from Bob Dickinson, senior vice president, sales/marketing. That's good advice for last-minute planners.

Carnival's prices will be 9 percent higher than last season. It still has space for a Christmas sailing but not for the New Year's departure. Changes are coming in 1982 with the introduction of a new ship, the Tropicale, sailing weekly. The itinerary of the Mardi Gras will change to the Western Caribbean ports of Cozumel, Grand Cayman and Ocho Rios, actually starting with the Dec. 20 and 27 sailings.

The line estimates that at least 130 out of 169 sailing hours will be spent at sea, something the passengers prefer. Air/sea add-ons, "Fly-Aweigh," will cost less in 1982. They will be $140 for this area, which is $15 less than at the present time.

Cunard Line Ltd., New York City, has announced an overall price increase of 13 percent for Caribbean sailings out of San Juan on the Cunard Countess and Cunard Princess. However, Cunard has lowered its air/sea add-on rates which are now two-tiered, geared to the type of shipboard accommodations selected. For this area, it is $99 for the higher-priced cabins and $149 for the lower-priced ones.

The line also will offer free one-way air fare on segments of its 1982 World Cruise, provided a trip of 17 days or longer is booked.

Cunard continues to offer free round-trip air fare with its two-ship cruise idea and "Sail 'n Stay" packages, combining a week's cruise from San Juan with a week at a Caribbean resort.

Holland America Cruises, New York City, is promoting a fly/free feature with its 17-day Thanksgiving Day cruise and for a 17-day Christmas-New Year's cruise aboard the Rotterdam, sailing from New York. In 1982 the line will offer fly/free on all cruise programs already in effect in this area.

An extra bonus on Florida sailings is a free three-day/two-night stay at the Fontainebleau Hotel on the pre-Christmas 11-day cruise on the Statendam and 12-day Volendam cruises.

Norwegian Caribbean Cruises, Miami, unveiled new programs in 1982 for three of its five ships, based on a recent $500,000 market research project. Two ships will call at Nassau instead of Puerto Plata, and one ship will have a complete itinerary change, going to Playa del Carmen, Cozumel and an Out Island.

In 1982, air/sea add-ons will be priced lower than the current ones, but the line's air/sea package price increases by 7 percent.

Paquet Cruises, New York City: Overall prices have been increased almost 10 percent. The Mermoz, sailing out of Miami, will do the Mayan cruises in 10 days instead of 11, and the Enchanted Islands sailings will go to 11 days from 10, adding a new port of call, Antigua.

Air/sea add-ons for this area will be $115 for the 10- and 11-day cruises and $215 for the 14-day Christmas cruise, sailing Dec. 20.

Royal Caribbean Cruise Line, Miami, offers a balance of western and eastern Caribbean ports on seven-day cruises, a change over last season. Rod McLeod, vice president of sales/marketing, says the line will guarantee current cruise rates through June 19, 1982. Prices already have been increased 12 percent.

Royal Caribbean is offering free round-trip air fare from all gateways including Washington on 14-day Nordic Prince cruises, effective Oct. 10 through June 19, 1982, excluding the Christmas sailing.

Air/sea add-ons for seven-day cruises are $165 for this area.

Sitmar Cruises, Los Angeles: The line's Fairwind, sailing from Port Everglades, will add St. Croix to its 1982, 10-day itinerary. The line also is adding the Isle of San Andres to the 11-day Caribbean-Yucatan itinerary.

Air/sea add-ons for the 7-, 10- and 11-day Caribbean cruises this fall will be $100 for Washington and Baltimore; while the 14-day and trans-Panama cruise offer a fly-free feature. In 1982, all Caribbean and trans-Panama cruises will have a fly-free offer.

Cruise fares next year will be 14 percent higher. Advance reservations of six months are recommended but the line will take them two months before sailing.

Costa Cruises, New York City. "Costa is offering several fall cruise promotions for those in the Washington-Baltimore area," said Paul Duynhouwer, senior vice president of sales/marketing. "On our four-day Bahamas cruises from Port Everglades aboard the Amerikanis, we are adding two free hotel nights at either Orlando or Fort Lauderdale. This will be available Sept. 14 through Nov. 23."

Duynhouwer also said that a second person in a cabin on a Caribbean cruise from San Juan on the World Renaissance will fly free round trip from D.C. or Baltimore, while the first person will pay $245 add-on for the round-trip flight. That offer will be in effect from Oct. 17 through Dec. 12.

Additionally, the Carla C, also sailing weekly from San Juan to the Caribbean, will offer a discount cruise fare of $100 each for the third and fourth passengers occupying the same cabin, from Oct. 10 through Dec. 12.

All lines considered, this fall and winter Caribbean cruise season is shaping up as one of the best buys in travel.

Shemanski is a free-lance writer with an extensive background in travel. She lives in New York City.