The crash of Flight 90 during a snowstorm has given pilots new respect for the hazards of winter flying, but to date has caused virtually no significant changes in the design of airliners or rules by which they are flown.

The accident had a positive effect of rekindling old debates on how pilots conduct takeoffs, how the Boeing 737 performs in icy weather, and how planes are certified as airworthy, aviation specialists say. But what, if any, changes will result is not clear.

The most tangible change has come locally, where rescue units have moved to improve equipment and coordination after finding they were ill-prepared to deal with the crash.

After a seven-month investigation, the National Transportation Safety Board ruled last August that the prime cause of the accident was the pilots' failure to observe elementary rules of winter flying.

They took off with ice on their wings, the board concluded, which altered the airfoil and reduced the lift generated. They failed to use engine anti-ice devices, which caused the throttles to be set too low, and they did not abort despite signs of trouble. 'Don't take off with snow and ice on the wings'--that is the prime lesson of the crash, says Anthony J. Broderick, a Federal Aviation Administration official.

"Don't take off with snow and ice on the wings"--that is the prime lesson of the crash, says Anthony J. Broderick, a Federal Aviation Administration official.

Consequently, the FAA's preventive efforts since the crash have focused on raising awareness of existing rules, not writing new ones. On FAA orders, pilots around the country were prepped on icing hazards, ways to use de-icing fluids, and when to turn on engine anti-icing devices and other basic rules of winter flying.

Experts feel these efforts and publicity in aviation journals have made flying safer, though there is no way to prove it. "Pilot attitude has changed," says a 737 pilot. " . . . That accident report has been the best-read accident of any of the publications that have come out."

Disagreement continues as to whether the design of the 737, one of the most common airliners in service, played a role in the accident. Before the crash, Boeing had advised airlines of reports of 737s pitching up at the nose suddenly during icy flying and suggested steps pilots could take to counteract it.

Air Florida, citing this alleged pitch-up tendency as the prime cause of the crash, announced after the crash that it would require its 737 pilots to use extra speed and different flap settings when taking off in icy weather, to provide an extra margin of safety. That is one of the few specific changes that the accident has brought about to date.

The safety board ruled that 737 pitch-up was a contributing but not a primary factor in the crash. But the FAA says there is no proof that the 737 is more prone to pitch up than other sweptwing jets.

After Boeing completes wind tunnel and other tests, the FAA will decide whether steps like Air Florida's should be mandatory for all 737 operators. Some sources say some 737 captains at other airlines unofficially have already begun steps like Air Florida's.

Boeing and the FAA are also looking at modifying the 737 so that pilots could heat up the wings just before takeoff and melt any ice that had accumulated.

In a letter sent to the FAA yesterday, the board expressed concern that any FAA action on the 737 "will not be timely for the current cold weather season" and reiterated its belief that interim steps are needed pending completion of the research. The letter was another reflection of often-opposing views between the FAA and the safety board, which has no enforcement powers.

The Washington accident and the Jan. 23 crash of a World Airways DC10 at Boston's Logan International Airport, which left two missing and presumed dead, led the board to conduct hearings into use of icy runways. Last month, it issued 18 recommendations, calling for better information on runway conditions for pilots, new methods for pilots to monitor takeoff acceleration and improved testing of how planes are certified to operate in slippery conditions.

The Air Line Pilots Association welcomed the recommendations, a spokesman said. The FAA has not formally responded to them yet.

In the safety board's final accident report last August, it also sought changes in air traffic procedures that it said made National congested the day of the accident and caused long waits for takeoff, during which ice built up on the 737's wings. The FAA turned down the suggestion, saying National operates safely and no changes are needed.

In addition, the board found that National's controllers had let an Eastern Airlines jet get too close to Flight 90, though the board did not say this was a cause of the crash. It requested changes in air traffic rules and in its letter yesterday said language the FAA had proposed did not address the issue.

Civic groups that maintain National is inherently less safe than the larger Dulles International and Baltimore-Washington International airports released their own report on the crash yesterday, which they said was prepared in consultation with pilots and other aviation experts.

It laid heavy blame on the airport. Flight 90's pilots were forced to lift off because National's comparatively short runways and overrun areas made it impossible to abort safely, the report by the Coalition on Airport Problems argued. The longer runways at BWI and Dulles would have let the plane stop or make an emergency landing, it said.

The board placed no blame on National's runways. The FAA has said that National fully meets applicable safety standards, noting the crash of Flight 90 was the first major accident there since 1949. The 737 is designed to use runways that are shorter than National's 6,870-foot main runway, the FAA says.

CAP also said congestion at National "has reached unacceptable and dangerous limits." It called for a 50 percent reduction in flights there, while continuing to maintain that safety would be best served by closing the airport to jets altogether.

The board is still looking at National as part of a larger study of safety at 14 U.S. airports and will issue a report later this year.

For area rescue units, the crash demonstrated that they lacked the boats and proper radios and coordination for a disaster of that scale. Yesterday, after a year of study, the Council of Governments approved an area-wide plan to improve coordination and communication in such an event.

The D.C. Police Department got a military surplus "Huey" helicopter late last year. Fire Department commanders have also acquired new radios with "mutual aid" frequencies that allow emergency conversations with other jurisdictions.

The airport, meanwhile, is moving to lengthen the runway overrun. It has also acquired rafts, three new boats, and other equipment since the crash and has sent 22 employes through Coast Guard disaster training. The FAA has resisted efforts to make it buy high-cost items such as boats and helicopters for local emergency units. But it has bought two nets to allow helicopters to fish victims out of water.