Months before an Air Florida Boeing 737 struck the 14th Street bridge during a snowstorm Jan. 13, British aviation officials began pressing Boeing unsuccessfully to support new takeoff rules designed to counter 737s' potentially dangerous tendency to pitch up at the nose occasionally during icy takeoffs.

Boeing opposed the changes proposed by the British, arguing that existing safeguards, if properly used, were adequate, a Boeing spokesman said yesterday.

But late last year, the British government unilaterally decided to impose the rules, requiring higher-speed takeoffs for all British-registered 737s in certain bad weather conditions. In a letter on Oct. 28, 1981, to one carrier, Britannia Airways, it said the action was needed "if we are not to see a future accident attributable to this cause."

The U.S. Federal Aviation Administration supported Boeing's stand and continues to do so.

Federal investigators have been studying whether a pitch-up helped cause Air Florida Flight 90 to crash after lifting off from National Airport, killing 78 people.

Air Florida argues that a pitch-up did occur, as has happened occasionally to other 737s in icy weather.

Boeing, which lays the blame largely on pilot error, says the evidence does not show any substantial pitch-up during the flight. The issue is one of several expected to figure prominently in damage suits filed after the crash.

The debate between Boeing and the British Civil Aviation Authority is detailed in letters, telex messages and notes on meetings obtained by Air Florida in pretrial proceedings for the approximately 60 suits filed in federal courts by crash survivors and relatives of victims. At least 27 other actions have been brought in state courts.

Suits have been filed on behalf of about 80 percent of the 78 people killed in the crash, according to George Tompkins, Air Florida's defense attorney. The widows of the pilot and co-pilot have filed suit. Four of five people aboard the jet who survived have filed suit, as well as three people injured on the bridge.

Pretrial depositions for the federal suits, consolidated at U.S. District Court in the District of Columbia, began this week, with discovery scheduled to end in January 1983. The suits variously claim that Air Florida, Boeing, the FAA and companies that manufactured products used on the plane were negligent.

The National Transportation Safety Board, which is investigating the cause or causes of the accident, is scheduled to consider final conclusions Tuesday, and lawyers will study the safety board's report closely. Though the board does not determine liability in accidents, its findings provide leads and raw data for the opposing sides in the ultimate apportionment of financial liability in an accident.

Since 737s entered service in 1968, at least 23 incidents of 737s pitching up or rolling to the side suddenly during icy weather have been reported to Boeing or appeared in the media. At low altitude, such events can be dangerous, because the crew has little room in which to recover control. However, none of the reported incidents resulted in a crash.

Boeing, which has issued bulletins noting the reports and recommending ways to avoid such incidents, has argued that it has worked diligently to correct any safety hazard that may exist.

Boeing's advice includes accelerating faster on the runway, being careful not to lift the plane's nose off the runway too quickly and applying controls gently if a problem does occur.

Buildups of ice on the wings also can cause control problems by altering the flow of air over them, and Boeing has reemphasized that wings must be checked before takeoff. "We still believe that having a clean wing is the answer," said Boeing spokesman Tom Cole.

According to documents provided by Air Florida, the CAA telexed Boeing in March 1981 that it was "very concerned" about two reports of 737s rolling and requested the matter be discussed with two CAA officials who were about to visit Boeing.

British officials later argued mandatory changes were required in takeoff procedures, not "advice" that could be ignored. Boeing argued its bulletins were adequate.

In the fall, the CAA announced it would require pilots of British 737s to do what Boeing had simply suggested: accelerate to faster-than-normal speeds on the runway in certain weather conditions, so as to generate extra lift. Boeing raised questions that the precise speeds the British selected might not be right, according to Cole.

In an Oct. 28, 1981, letter telling the chief pilot of Britannia Airways of the changes, CAA official D.P. Davies said: "We believe that tangible actions need to be taken rather than merely offering further advice, if we are not to see a future accident attributable to this cause."

Requiring a pilot to ensure the plane is ice-free at takeoff is not always practical, Davies said, because pilots cannot always see it, "particularly at night and at busy airfields where significant pre-takeoff delays can occur."

Requiring higher takeoff speeds will have "an adverse economic effect" on airlines, the letter said, because some planes would be forced to carry fewer passengers or less fuel, forcing additional stops for fuel. But he said the cost was worth "the significant safety improvement which will result".

The order was made official two days after the Air Florida crash (CAA officials say the timing was coincidental).

In June, it was expanded to forbid bad-weather takeoffs with the planes' flaps in certain positions which the CAA believes makes them vulnerable to coating by ice. Boeing opposed such a move. "We're not at all sure that flap settings are going to solve the problem," said Cole.

In a decision also related to icing, Boeing has announced that it might modify 737s to allow airlines to use wing ice-melting devices on the ground before takeoff. That would reverse current procedures to use them only in mid-air against ice formed during flight. In the past, ground usage was ruled out because it can damage a wing.

Cole said that the new method is intended to give pilots an alternative to increasing their runway speed or other steps recommended in the bulletins. It would provide one more protection against ice on the wings but would not replace visual inspection, Cole said.