THERE'S GOOD news in the air for jet travelers who know that the Washington area has two excellent international class airports (Dulles and BWI) and who wish they had less need to go to New York in order to fly abroad.

There's also good news for "full-fare" coach passengers, according to some airlines which have begun providing extra service and comfort to those customers who are paying more for their seats - though the idea might wind up rankling some "discount" passengers, and perhaps may disturb some non-smokers.

And every U.S. resident returning from international travel can find good news in the recently passed Customs Procedural Reform and Simplification Act of 1978.

Let's review those three items in order:

Caribbean Airways and Icelandic Airlines are each taking off in the right direction, beginning this month. In both cases, Baltimore-Washington International Airport is the department point.

Caribbean, the national airline of Barbados, inaugurates non-stop Boeing 707 service on Nov. 16. Flights will leave BWI at 12:45 p.m. each Thursday and (beginning Dec. 17) Sunday, with return flights departing Barbados at 8 a.m. on Thursday (and, in December, also on Sunday).Caribbean Airways, whose industry code letters are "I.Q.," points out that the easternmost island in the West Indies, an independent member of the British Commonwealth, has "one of the highest literacy rates in the world."

They might also have added that East Cost residents with sufficient I.Q.s - and cash - quickly recognize that the Caribbean sun performs miracles in winter.

I.Q. "has relied on the technical expertise of a minority shareholder (Freddie Laker's Laker Airways; with 49 percent) for much of the operation of its services," the airline says. And almost everybody knows Sir Freddies even if they don't know I.Q. yet. Unlike Sir Freddie's bare-bones transatlaptic flights, however, I.Q. will serve a "rum punch, hot luncheon with complimentary wine and high tea." Until rates change in December, the G.I.T. (Group Inclusive Tour package) round-trip air fare will be $190, with an all-economy 185-seat configuration.

Icelandic, which was offering low-cost transocean travel long before Laker, yesterday began a once-a-week round-trip flight to Luxembourg, using the McDonnell-Douglas stretch DC-3 that carries 249 passengers.

Officials said that the schedule calls for a second flight, on Thursdays, to start April 5, assuming there is sufficient demand, and possibly a third in May. The current single BWI departure is now on Saturday evening with a Friday afternoon return departure from Luxembourg (the Friday departure changes to Thursday in April). The single-class, round-trip fare is $310. There is a 45-minute stop in Reykjavik Iceland, and passengers have layover privileges. They can also buy one-way tickets.

BWI thus has "its first direct transatlantic European air service in more than three years," according to the Maryland Department of Transportation. Karl R. Sattler, the state's aviation administrator, said Icelandic officials were "especially impressed BWI's growth and modern passenger terminal facilities, its ability to attract passengers from both sides of the Washington/Baltimore market, and the excellent domestic connecting services at BWI which are able to feed the international flights." BWI expects to reach a total of about 3.4 million passengers this year.

Icelands has announced that, beginning in January, it will also offer low-cost European ski programs, using the BWI service, "starting at $447 a week" including air fare. The return trip will be via New York, continuing to BWI via connecting airline.

Dullas Airport now handles about 10 international flights a day, according to manager Dexter P. Davis. "Growth in traffic has been fairly substantial," Davis said, with 556,815 scheduled international passengers and 56,101 non-scheduled (charter) international departures are now offered by British Airways, Pan-American, TWA, Air France, Aeroflot and Braniff, Davis said. Dulles had a 12-month total in August of 3,109,670 passengers.

The full-fare or three-class service was introduced last month by American Airlines and Trans World Airlines - and was promptly followed by Pan American (Clipper Class), British Airways (Club Class) and Air France versions. United Airlines adopted a wait-and-see attitude, while Eastern Airlines indicated it will not go along because it believes the idea will prove to be a costly mistake. Other airlines were silent about their intentions.

Simply stated, all full-fare plans were prompted by a rising crescendo of complaints from business travelers, who protested that the new discount fares had resulted in "crowded airports, longer lines, slower service aboard the plane, etc.," as TWA put it in a recent trade publication ad.

These disgruntled businessmen knew very well that they often were paying twice the fare of the passengers in adjoining seats. Since American Airlines management (and others) believe that the "full-fare passenger continues to be 'bread and butter'" of their business, it was natural for them to try to satisfy the complainers.

Basically, what the five lines have done is to divide the coach cabin into two sections - the front portion for passengers paying full fare and the rear portion for those with discount tickets - thus creating three classes of service.

Full-fare passengers, on the ground, can have their seat selection when they make reservations, can get round-trip boarding passes when they check in, and can use separate check-in facilities. Once aboard the plane, they sit in a separate (marked by signs but not physically partitioned) section surrounded only by their full-fare competitors, and are served beverages and meals ahead of their poor relations in the rear seats comfirming the economy (third) class section. If there's a choice of entrees, they'll get first dibs.

The airlines say that if there are any empty seats, they more likely will be in the full-fare section, giving those passengers the bonus of extra elbow room. But Travel Weekly reported that on American's first day of service out of New York, a full-fare passenger who was surrounded by occupied seats saw that there were empty seats in the thrid-class section and asked for a partial refund. He didn't get it.

While a Civil Aeronautics Board spokesman said last week that it's possible some discount passengers who was surrounded by occupied seats saw that there were empty seats in the third-class section and asked for a partial refund. He didn't get it.

While a Civil Aeronautics Board spokesman said last week that it's possible some discount passengers may complain to the board, he added that they need to remember "the extras are not really part of the price you pay - they're up to the airlines. Basically, in the past you had only service competition, but no price competition. Now, with deregulation, the consumer has both price and service competition to look at.

"The world has become more complex," the CAB spokesman added, "and it's now up to the consumer to know what questions to ask travel agents and airlines and to find out options."

Another possible controversy involves the still unresolved question of whether to continue to permit smoking aboard aircraft and, if so, what kind and how. The same total number of non-smoking seats are potentially available on any full-fare configuration flight, but some non-smokers have already pointed out that they now find themselves surrounded by smokers due to the fact that the cabin has been further divided up. What is the CAB's position?

Nothing that smoking is "a very sensitive issue on both sides," the spokesman said that current CAB regulations concerning non-smokers' rights are still "not crystal clear," though most U.S. airlines are interpreting the rules to mean that while smokers can indulge, they may not do so when that action infringes upon the "rights of non-smokers not to ingest others peoples' smoke."

In practice today, this means that if you and your family are at the tail end of the discount third-class check-in line, and you tell the seat-selection agent that you want four seats in non-smoking, the airline should not tell you that there are no more non-smoking seats available. If necessary, the airline should move the "smoking" sign to accommodate you family, even if that means some passengers already seated in the "smoking" section will then find themselves "moved" to the non-smoking portion of the cabin and will be unable to light up. But advocates of stronger non-smoking rules or an outright ban maintain that, despite statesments by pro-smoking advocates, it is not possible to properly ventilate an aircraft and remove tobacco fumes. The airlines thus remain in the middle.

The long-awaited final order that was aimed at banning pipes and cigars aboard aircraft was still being drawn up by the CAB staff when the composition of the board began to change, the spokesman explained. This left "one member for and one member against the ban." A revised proposal is now being prepared for consideration by the new board, he said. "Three out of the five members will have had no previous discussion of the smoking issue."

U.S. Customs regulations, effective last Thursday, allow each U.S. traveler returning from abroad to bring back $300 in duty-free purchases ("based on the fair retail value in the country of acquisition"). The previous personal exemption was $100.

From U.S. insular possessions (the Virgin Islands, American Samoa and Guam), each returning traveler now has a $600 exemption from U.S. duty (instead of $300) - provided not more than $300 of those purchases have been acquired outside those islands.

In addition, Customs is assessing "a flat duty rate of 10 percent (5 percent for residents returning from insular possessions) on the first $600 worth of goods over the standard $300 or $600 exemption." The Treasury Department says "this will eliminate time-consuming duty calculations and speed U.S. residents through inspection lanes."

For complete information on charges in the law, write to U.S. Customs, P.O. Box 7118, Washington, D.C. 20044, and ask for a fact sheet on the new regulations and also the leaflet, "Know Before You Go."