Federal Aviation Administrator J. Lynn Helms has cited cost as the reason for rejecting two major safety recommendations that resulted from the nation's worst airline disaster.

The recommendations from the National Transportation Safety Board concerned maintenance difficulties discovered after an American Airlines DC10 crash in Chicago on May 25, 1979, that killed 273 people.

One of the recommendations would have required FAA inspectors to monitor airline maintenance to assure that problems learned by one airline in the operation of a type of airplane would be shared with other airlines.

The other would have required FAA inspectors to review any damage inflicted during maintenance that would be "structurally significant" and to share that information with other airlines.

In the DC10 crash, a maintenance-caused crack in an engine support led to the failure of the support and the crash.

Investigators learned that, months before the American crash, Continental Airlines mechanics had induced the same failure, using the time-saving maintenance procedure American was using.

Continental fixed the crack before returning the airplane to service. The Continental discovery was not widely shared among the airlines.

Further, the FAA inspectors were not notified of the damage to a "structurally significant" component.

Helms told the safety board that he was rejecting both recommendations because "additional reporting requirements would cause an economic burden without yielding a corresponding increase in safety benefits."

The principal burden would apparently be on the FAA, which has been under substantial budget pressure.

The FAA's maintenance inspection program delegates much authority to the airlines, which are also having tough times economically.

The FAA earlier had proposed to adopt the board's recommendation on "structurally significant" maintenance damage, but has changed its mind, Helms said. The board said that change "is disappointing and perplexing."

The rejections came last October in a letter from Helms to Safety Board Chairman Jim Burnett. The letter, which discussed many recommendations stemming from the DC10 crash, was made available along with the board's response, dated Tuesday.

A maintenance error caused all three engines on an Eastern Airlines L1011 to run out of oil and fail earlier this month. The crew was able to restart one engine and return to Miami to avoid ditching in the Atlantic Ocean.

The error followed a series of similar occurrences at Eastern and a related difficulty at Pan American World Airways. Pan Am changed oil system fittings on its L1011s to fix the problem.

The FAA inspector responsible for Eastern maintenance did not know of the Pan Am change until after the May 5 incident, when he started asking around among others in the industry.