Officials of more than 125 airlines have been invited to a meeting at the Department of Transportation later this month to begin discussing the possibility of shifting some flights from Washington's National Airport to the area's other two airports.

The Civil Aeronautics Board gave the airlines antitrust immunity last month to begin such discussions, but until now no steps had been taken to get the discussions moving.

The DOT's invitation came in the form of a letter from General Counsel John M. Fowler to officials of major, regional and commuter airlines, and some state and local governmental and airport officials.

In his letter, Fowler said Transportation Secretary Drew Lewis and Federal Aviation Administrator J. Lynn Helms were committed to the success of the discussions. "They believe that an agreement to shift substantial numbers of flights out of National either to Dulles International or Baltimore/Washington International airports will relieve the strain caused by excessive demand, and thus will permit more competition in all air services to and from the Washington area," Fowler wrote.

The prognosis for the talks is unclear. "The only thing that could happen is the movement of Florida flights out to Dulles," Edwin I. Colodny, chairman and president of USAir, guessed yesterday. USAir, a Washington-based airline currently operating 36 daily flights out of National, has very limited Florida service from National right now, just one nonstop flight and one one-stop flight. But Colodny added, "We'd be willing to move our service out there."

Florida routes have been considered a prime candidate for a move by some partly because there are so many flights--at least 30 nonstop round trips a day and additional one-stop and two-stop trips--from National. Also, it's believed that those going to and coming from Florida more often are taking vacation trips rather than one-day business trips. The flights also take between two and three hours. As such, Florida travelers may be more willing to spend extra time getting to or from the airport for their trips, the reasoning goes.

The DOT has scheduled a preliminary meeting for Jan. 26 to determine the scope of the discussions and procedural matters. Full discussions will begin on Feb. 16.

The CAB granted authority for the discussions in response to a petition from four airlines operating at National: Midway, Piedmont, Republic and USAir.