RELISH THE confusion that has resulted from the airlines' new fare flexibility and their growing new route systems as a result of increasing airline deregulation. It means a chance for lower-than-ever fares for a winter vacation even though the trend for regular air fares, as for most everything else, is up.

The next couple of months especially afford the traveler some bargains because airlines starting new routes -- both domestic and international -- are doing so with special promotional fares designed to attract attention.

In addition, because the winter months are traditionally slow in the travel business -- except for beach and skiing resorts -- many of the airlines offer attractive fares to those travelers willing to take the time (and yes, the trouble) to find out the cheapest way to get some place, even on relatively short, or no, notice.

Some of the low fares can get you to sunnier, warmer places than Washington. Air Florida, which picked up an unused route of another airline through a procedure set up by the recently enacted Airline Deregulation Act, offers travelers the lowest regular fares to Florida from here. They are $53 to Ft. Lauderdale and Miami on Monday, Tuesday and Wednesday, and $80 the rest of the week, compared with a regular coasch fare of more than $100 each way. A Super Saver discount fare during the nonpeak travel days on Eastern and National Airlines can afford a similar savings, but the traveler has to plan at least seven days in advance -- and seats are limited at those prices -- to take advantage.

Although new route authority already granted and soon-to-be granted by the Civil Aeronautics Board will increase the number of airlines -- and perhaps the fare options -- to the Caribbean area, not much new is off the ground yet. Caribbean Airways, however, has recently started nonstop service to Barbados from Baltimore-Washington International Airport.

The Mexican Caribbean is an exception. Both Texas International and Eastern Airlines, for instance, have new authority to cities on the attractive and interesting Yucatan Peninsula. Although in-season rates apply now, recent travelers to Mexico report that, because of the devalued peso, the American dollar goes further there than in most Caribbean or other sunny climes.

Even though the United States and Mexico not too long ago signed an air agreement that assured increased service and lower fares between the two countries, the Mexican government for a long time has encouraged American tourism so regular air fares to Mexico on a permile basis are about 30 percent lower than regular coach fares for comparable distances within the U.S., according to a spokesman for TXL. Most of the Mexican vacations are sold in packages including the air fare.

Travelers who want to stop more than one place may find Eastern's "unlimited mileage" fare a boon. For between $372 and $399 each, depending on the taxes of the routes chosen, two adults can pick any unmber of 105 cities in 12 countries served by Eastern they can cram into 21 days. Many Caribbean points are included, as are Bermuda and Mexico. Eastern flies to the far West and Northwest as well as all over the East, Midwest, and South.

Also eligible for the fare is one adult traveling with two or more children; the cost per child is between $202 and $215. There are restrictions attached to the fare.

Allegheny Airlines, which has begun flying to Florida from here and exsimilar unlimited mileage "Liberty" fare allowing adults to travel anywhere on its domestic system for $179 for between three and 10 days. Accompanying children pay $89.50.

For a warm and interesting nonbeach vacation, Pan American World Airways continues to encourage visits to Guatemala on its nonstop service from here as an alternative to using excursion fares.

To encourge domestic travel during the bleak winter months, Trans World Airlines thought up a new "Pair Fare" which entitles a person using a regular coach fare to take along a second adult for 50 percent off, with no advance purchase. Now matched by some other airlines, thefares are good in February and March.

To take advantage, the couple has to stay over a Saturday night and no more than seven days. Beginning Feb. 13, TWA proposes to offer the second adult -- if he or she is the spouse of the first passenger -- a 60 percent discount, and the trip can last up to 30 days.While a regular Super Saver discount can save the two travelers more money, the trip has to be planned and tickets paid for 30 days in advance and the stay must be at least seven days.

TWA also will allow each adult on a coach or discount ticket to take along one child under 12 free during February and March; they even get seats.

For more ambitious travelers, Pan Am still offers its "Round the World in Less Than 80 days" $999 fare for a savings of almost 50 percent off the regular coach fare. Winter is the ideal time to take this standby fare because of the slow winter travel business. A 35 percent discount off the regular fare entitles a traveler to areserved seat on a round-the-world jaunt.

Despite the lure of sun and sand, vacations to nonbeach places are ideal during the winter because of the low, off-peak fares and the off-season hotel rates.

Despite the weakness of the dollar, moderately-priced accommodations -- and even nice budget lodings -- do exist in Europe. A traveler could put together a vacation week or two in Europe that may cost half as much as it will next summer, and avoid the summer crowds as well. A traveler can get to London and other major European cities using low fares -- even standby -- with relative ease now.

From Washington this winter, for instance, a traveler can go to London standby and back for $299 on Pan Am; the airline also offers the "Budget" fare of $289 roundtrip for passengers who are willing to pick the week of travel at least three weeks inadvance and let the airline assign the date and flight.

British Airways and Trans World Airlines have some similar, and some of the same, fares. All three also offer an advance-purchase fare of $329 roundtrip for passengers who want to select the exact day and time for their flights and can do so three weeks in advance. The trip must last between seven and 60 days.

Don't forget Sir Freddie Laker, the Britisher who started the current transatlantic air fare war with his noreservations Laker Skytrain. His New York to London fare is still the cheapest; it hasn't changed since he started service in September, 1977. It is $135 to London and 59 pounds back (about $120). If leaving from New York is no trouble for you, Laker should be considered a real possibility.

Some other transatlantic highlights this winter:

Icelandic Airlines, a pioneer of low fares, flies from BWI to Luxembourg for $310 roundtrip.

National Airlines is offering passengers a $300 roundtrip ticket from Washington to Amsterdam ( with a change of plane in New York) to usher in its new service.

Trans World Airlines and E1 A1 have fares to Israel for $532 from Washington, the lowest-priced scheduled air service there has ever been for that route.

Although the standby transatlantic fares stand alone, other fares can be combined with tours and ground packages that may afford the traveler both the savings and the convenience of someone else's planning. In its 10th year now, for instance, Pan Am's one-week London theater tour is the most successful package the flag carrier has ever offered.

As a result of recently signed bilateral agreements with Germany, Belgium and the Netherlands, new services and new low fares may materialize in the relatively short future. Because of the continuing changes in the domestic and international aviation picture spurred by pro-competition U.S. policies, the diligent, comparisonshopper may be able to turn up unexpected bargains this winter or a trip to a place once considered just a dream.

Call airlines and travel agents to find out what's available. Although one isn't required to use a travel agent to book flights or packaged tours of the scheduled airlines, the travel agents -- who get their commissions from the businesses, not the travelers -- may know of some tours and charter packages that would not turn up with calls to the airlines and they can give free, helpul advice.