The Federal Aviation Administration has rejected as unnecessary or improper several safety recommendations that the National Transportation Safety Board said were key to correcting problems that contributed to the Jan. 13 crash of an Air Florida jet at the 14th Street bridge.

In a letter this week outlining its position on the recommendations, the FAA concurred with some board proposals involving renewed emphasis on existing safety procedures and water rescue preparations, but turned down other suggestions.

By law, the FAA is not required to adopt safety board recommendations, only to respond to them within 90 days. The agency has traditionally disagreed with the board over certain principles of aviation safety and has often rejected its proposals.

The FAA's letter, written Nov. 15, came in response to 11 recommendations issued by the board Aug. 11, after a seven-month investigation into why the Air Florida jet crashed in a snowstorm 30 seconds after taking off from National Airport. Seventy-eight persons died in the crash.

The safety board placed primary blame for the crash on pilot error, but recommended changes in some procedures it said contributed to the accident.

The board proposed changing takeoff procedures for Boeing 737s to correct what it called the jets' "known inherent . . . characteristics" to pitch up at the nose or roll without warning if "even small amounts of snow or ice" are on the wings' leading edges. The board found that such a pitch-up contributed to the crash, but was not a direct cause.

In the letter to safety board Chairman James Burnett, FAA Administrator J. Lynn Helms said his agency "has not yet determined if the B-737 is, in fact, more sensitive than other airplanes to the pitch up/roll off phenomenon." He said any action should await completion of wind tunnel tests that Boeing is now conducting with FAA participation.

The board proposed requiring that 737 pilots include engine anti-icing devices in the "check list" they run through before take-off. The FAA agreed to a general review of checklists, but declined to make inclusion of the anti-icing devices mandatory, saying existing regulations are adequate.

The board called for improvements in the FAA's management of traffic levels, saying that traffic congestion at National that day contributed to the crash by creating long delays during which snow and ice collected on the Air Florida plane.

Helms said the FAA performed with "good operating technique" that day and declined to make changes.

The board, concluding that controllers in National Airport's tower violated air traffic rules by letting an Eastern Airlines jet land too close behind the Air Florida jet, requested the FAA take action to assure that did not recur.

Controllers had said they followed the rules as they understood them. In his letter Helms proposed new wording for the air traffic handbook that appears to support the controllers' reading of the regulations.

The board also called on the FAA to improve preparation for accidents at National and to "provide necessary funding" to local governments that would assist in rescue efforts. Helms responded that National, which the FAA owns and operates, has been improving its capabilities, but said local governments must buy their own equipment, or the FAA would be deluged with requests for aid.

The FAA agreed in part or in full to the following recommendations from the board:

* Pilot training courses should stress the dangers of flying with icy wings.

* The FAA should stress to airlines that ground equipment must be in good repair and that contract maintenance crews must understand their duties.

* Controllers should be reminded to report all near misses and other air traffic errors.

* The FAA should survey existing water rescue plans at airports with flight paths over water and suggest any needed improvements and amend regulations to require that such airports prepare for water crashes