Air traffic to National Airport declined last year while Dulles and Baltimore-Washington International airports experienced hefty increases, according to statistics released yesterday by the Federal Aviation Administration.

For years, residents of the Washington area have expressed their displeasure at the heavily overcrowded National, but it has been only in the past year that there have been enough flights at Dulles or BWI to meet demand.

"We are seeing a significant movement in the regional market as a result of the growth at Dulles," said Clark Onstad, vice president of Texas Air, whose subsidiary New York Air has been a major player at Dulles. "When the public is confident that an airport will have reliable and abundant service they flock there."

And they have. Dulles had 5.4 million passengers in the 12-month period through February -- a 56 percent jump over the previous year. BWI enjoyed a 17 percent jump in passengers -- to 7.8 million in the 12 months through February. During the same time period, National's passenger total declined 1.2 percent, although it is still the dominant airport in the region with 50 percent of the passengers.

Dulles has been steadily increasing its percentage of the regional air market for several years. In 1982 a survey conducted by the Metropolitan Washington Council of Governments showed that 20 percent of passengers at National -- about 2 million people -- would have used Dulles if there had been flights to accommodate them.

The COG survey indicated that if passengers could use any airport they wanted, about 50 percent would use National, and the other passengers would be split evenly between BWI and Dulles.

According to statistics compiled by the FAA, in 1981 BWI had 19 percent of the region's air travelers, Dulles had 11 percent and National had 70 percent. In 1983, those figures had changed to 23 percent for BWI, 13 percent for Dulles and 64 percent at National. By last year, BWI had 27 percent of the market, Dulles had 23 percent and National had 50 percent.