The California naval air base that aroused controversy over its purchases of $659 aircraft ashtrays paid the same defense contractor to fit F14 fighter planes with a $529 seat cushion and a $3,782 valve, according to Navy investigators.

The investigators who examined spare-parts purchases at Miramar Naval Air Station near San Diego concluded that prices were "unreasonable" for half of the items surveyed, according to a Navy report obtained yesterday.

In a separate investigation, the General Accounting Office found that while Miramar was paying Grumman Aerospace Corp. for the cushion and valve, the same items were sold by Grumman to the Navy's aviation supply center for $123 and $1,280, respectively.

Both investigations began in June following reports that Miramar had paid Grumman $659 each for the ashtrays and $404 apiece for socket wrenches. Two officers at Miramar have been dismissed because of the overpricing.

Miramar's purchasing practices will receive their first congressional airing today before the House Government Operations Committee. Chairman Jack Brooks (D-Tex.), who requested the GAO review, said the problems stem from Miramar's preference for dealing with a single contractor instead of competitive bidding.

Brooks cited one example in which Miramar paid Grumman $87.55 for a self-locking nut in January. Other vendors would have charged the Navy $18.19 each if the nut was purchased in larger quantity, he said.

"These are just examples of the Navy's wasteful purchasing practices," Brooks said. "They're just throwing away the taxpayers' money."

A Navy spokesman said the findings may be misleading because the surveys focused on a relatively small percentage of Miramar's annual contracts.

Joseph Vranich, a Grumman spokesman, defended the $529 price for the cushion, saying it takes 6 hours of labor to produce. He said Grumman has no record of a less costly cushion that GAO contends was sold to the Aviation Supply Office.

He was unable to explain why the valve sold directly to Miramar was three times the price of the same item sold to the aviation supply center. But he said it was among the spare parts Grumman suggests the Navy buy elsewhere.

Navy investigators, sent to Miramar in early June by Navy Secretary John F. Lehman Jr., examined 78 spare-parts purchases, comparing the price of each item with its market value. Thirty-nine items were deemed to be overpriced, according to the report, including:

*$1,060 to Grumman for an indicator light for F14 planes, which should have cost $116.

*$288 to Pratt & Whitney for a socket wrench, which should have cost $50.

*$514.80 to Hazeltine Corp. for an aircraft block, which should have cost $40.

$39.71 to Glenair Inc. for an adapter cable, which should have cost $5.

GAO investigators, examining Miramar's records at the same time, focused on 20 spare-parts purchases. In three cases, Miramar failed to buy items from vendors who offered them at "significantly lower" prices, the report said.

According to a congressional source familiar with the GAO report, Miramar paid Grumman $1,143 for an indicator light in February. Midland-Ross Inc., which manufactures it, priced it at $330 at the time, the source said.