A proposal to allow wide-body jets to use National Airport would result in "unacceptable risks to pilots and passengers," the Air Line Pilots Association told a congressional hearing yesterday.

The introduction of the newer, quieter jumbo jets, some capable of carrying 380 passengers, has been proposed by the Federal Aviation Administration as part of a plan to reduce the number of takeoffs and landings at National.

The agency has said its plan would meet the growing demands of passengers who like the convenience of the airport and the outcries of residents angered by the roar of planes in its flight paths. The FAA also maintains that use of the jumbos at National would be safe.

John J. Ruddy and Lawrence A. Horton, ALPA's two top safety coordinators for the Washington area, told the House subcommittee on aviation that neither the wide-body planes nor National Airport alone are unsafe.

"But we believe the combination . . . will mean an acceptable level of safety cannot be assured with reasonable confidence," they said.

The big problem, they said, is that the jumbo jets cause a "wake vortex" problem for other aircraft following in their flight paths. Wake vortex is horizontal, tornado-like turbulence geneerated at each wing tip.

Among ways to avoid the wake vortex of a jumbo jet is to stay up to 10 miles behind it, or maneuver around it, but restrictions on where planes can fly in the crowded airspace surrounding National make those actions dangerous, they said.

In bad weather, the Potomac River approach to National, flying south over the river near Georgetown and Rosslyn, "is one of the most difficult and demanding approaches in the U.S.," said Ruddy and Horton, who together have more than 50 years of experience flying into National.

The question of safety overshadowed other concerns voiced during the day-long hearing about traffic congestion, noise pollution and takeoff and land curfews at National.

Rep. Joseph L. Fisher (D-Va.) said facilities at National "already are outdated, overcrowded and increasingly dangerous."

The FAA plan to allow the number of passengers using National to increase from its current annual 15 million to 18 million by 1990 would pose "a severe safety hazard," warned Fisher, who did not limit his concern to wide-bodies.

"I would hate to wait until there is a terrible accident to transfer" some flights to Dulles, Fisher said.

The FAA which operates both National and Dulles airports, was not represented at the hearing. But a spokesman said later that "before we even proposed the use of two- and three-engine wide-bodies at National, our Office of Aviation Standards thoroughly reviewed the safety aspects of the wide-bodies, and was satisfied that their operation in and out of National was indeed safe."

Pilots Ruddy and Horton said the only test landings of Jumbo jets at National were "purely cosmetic demonstration flights of the A300 and DC10 in the fall of 1978," which they said were carried out under ideal weather conditions.

With the aid of films produced by the FAA and NASA, Horton showed that the wake vortex of a DC10 was powerful enough to shake and throw off course planes as large as twin-jet DC9s or Learjets trailing the jumbo by as much as five miles.

"The larger and heavier the aircraft, the larger and more violent is the vortex," said Horton.

Ruddy said that in May 1972 a DC9 -- a widely used medium-range passenger jet -- was following a DC10 onto a runaway at Fort Worth during a training flight, went out of control and crashed because of the Jumbo's wake vortex.

"It is only logical that wide-body flights and future traffic growth should be limited to Dulles and Baltimore-Washington International airports," the pilots said.

Subcommittee chairman Glenn M. Anderson (D-Calif.) asked the spokesman for the nation's major airlines, Norman Philion, what his organization thought about the safety question raised by the pilots.

"The final decision should be made by the airline industry and the airport manager, after permitting the two- and three-engine wide-bodies to demonstrate their ability to operate at National," said Philion, who is executive vice president of the Air Transport Association.

Philion said after the hearing that the jumbos are "operating safely at every other major airport in the country."

The use of wide-bodies at National, as one way of reducing the number of daily flights, was either supported or not opposed by the half a dozen area members of Congress and a dozen other local officials or representatives of citizens' groups who testified. But most of them spoke before the pilots raised the question of safety.

One idea that was supported by Fisher and several other witnesses was the removal of National and Dulles from the jurisdiction of the FAA.

Neither the transfer of authority nor reduction of flights will come without a battle. Rep. Marilyn Lloyd Bouquard (D-Tenn.), a member of the subcommittee, has gathered the names of more than 70 House members on a resolution that opposes any reduction in service at National, and several of them will testify when the hearing resumes this morning.