The Federal Aviation Administration said yesterday it intends to fine Pacific Southwest Airlines a record $385,000 for what it called a "pattern" of maintenance violations that in some cases may have caused PSA to fly passengers in "unairworthy aircraft."

PSA vice president James Snoddy said he was "appalled" by the charges and that "there is absolutely no basis for them. We feel we can refute each and every one of them."

The FAA's intent was made known yesterday in a six-page letter to PSA president William R. Shimp. Ten specific violations of federal air regulations were cited, including charges that some of PSA's planes were flown in an unsafe condition.

"We believe that these violations disclose a pattern by PSA to defer the immediate performance of required maintenance," the FAA letter ".... Moreover, "...Moreover, it appears that these policies caused PSA flight crews to conduct revenue flights (that is, passenger-carrying ones) in unairworthy aircraft."

PSA is a small airline - it has only 29 planes - but has been enormously successful in building a heavy schedule, almost entirely within California. It has consistently undercut the fares of big-name airlines in the West. PSA's success at attracting passengers with a combination of low fares and good schedules was frequently cited in Congress as an argument for deregulating airline routes and fares.

The enforcement action against PSA came as a result of a routine inspection by FAA employees, FAA chief counsel Clark H. Onstad said yesterday. It comes at a time of increasing concern about FAA monitoring of airline maintenance practices that has resulted from the investigation of the American Airlines DC10 jumbo jet crash in Chicago May 25 that killed 273 people.

According to both PSA and FAA officials, the PSA investigation predated the Chicago accident.

Several of the FAA allegations appear to pertain more to paperwork and record-keeping than to genuine air safety issues. Others, however, appear more serious.

The FAA letter charged, for example, that:

- PSA operated two Boeing 727 jets for a total of 135 flights when they had cracks in the forging in the main landing gear beam support lug. "In both instances, required maintenance was deferred," the FAA said.

- PSA permitted a jet with a malfunctioning tachometer to make 94 flights. A tachometer is the instrument pilots used to monitor engine performance and is essential during takeoff. It is illegal to fly without an operating tachometer.

- PSA permitted 13 flights of a jetliner with a defective engine that "would have delayed engine response to the application of power."

Art Smoak, PSA's director of maintenance, said in a lengthy telephone interview that:

- The landing gear lugs were not load-bearing, that the problem was not significant, and that PSA had the authority to make that determination. "We contend there isn't even a technical violation," he said.

- The tachometer in question did act erratically on one occasion, was checked by a mechanic and cleared. Subsequently, the tachometer stopped working completely and was replaced. No flights were made illegally, he said.

- The "defective engine" was "never out of operating limits, although it did have a slow spool (response) problem." Again, no flights were made illegally, he said.

Smoak said that one FAA complaint concerning record-keeping, not air worthiness, "could be a valid item."

PSA has 20 days to reply. Then there is an administrative appeals process following which the case could go into federal courts.