General Motors Corp. is having trouble supplying parts for a campaign to fix a flaw that could cause engine fires in Chevrolet Chevettes and Pontiac T-1000s sold in model years 1980 through 1982.

The parts shortage is delaying repairs and testing the tempers of dealers. It has also been blamed in a suit against GM by a couple in the Washington area, who say their 1981 Chevette exploded and burned two days after a dealer told them he did not have the part needed to do the recall-repair on their car.

Meanwhile, National Highway Traffic Safety Administration officials are investigating at least 160 car fires in Ford Motor Co. Escort and Lynx subcompacts, sold during the 1981 and 1982 model years.

Unlike the GM fires, the Ford fires apparently have a variety of possible causes, including possible electrical and mechanical malfunctions, NHTSA officials say.

There have been no reports of accidents or injuries in the Ford cases. NHTSA officials said yesterday that they have allegations of "four minor injuries" in 355 GM subcompact fires reported between July 1982 and mid-March 1983.

On March 19, GM sent recall letters to about 491,000 Chevette and T-1000 owners, advising them that a defect in their 1.6-liter engine cars could, "under certain conditions," result in "underhood fire."

"The carburetor fuel inlet housing plug may come out. If this occurs, fuel will leak from the carburetor and, under certain conditions, an underhood fire could result," the letter said in part. It added: "Such a fire could, in time, spread to the passenger compartment and cause burn injuries to occupants remaining in the vehicle."

GM said in the letter that a carburetor plug retainer clip was needed to secure the plug. The clip, a $1 item, would be available to dealers "approximately March 21, 1983," the recall letter said.

But area GM dealers surveyed yesterday said they had not yet received the clips, or only had small supplies of the parts.

"They are right. We've had a problem" getting the parts, John Hartnett, a GM spokesman, said yesterday. Hartnett and NHTSA officials said parts supply often lags behind the issuance of recall letters. But the GM situation was aggravated because the voluntary recall campaign for the subcompacts was expanded from 81,362 cars in October 1982 to 491,000 cars on March 11.

Suppliers who made the parts had laid off workers, many of whom had to be called back to produce parts for the expanded recall, according to Hartnett and other GM officials.

GM had 59,000 of the retainer clips on hand at the time of the expanded recall. Overtime shifts are producing additional parts at the rate of 80,000 a week, which means the company's 5,100 Chevrolet and 3,100 Pontiac dealers should start receiving parts in bulk within two weeks, Hartnett said.

The local lawsuit against GM was brought by Aklog Birara and his wife, Amsalnesh Woreta. Woreta, a Maryland Federal Savings and Loan Association employe, said she watched the 1981 Chevette explode and burn last Saturday at about 8:45 a.m. in the S&L's parking lot.

The car was bought new for $5,400 by the couple and had been driven only 8,000 miles use when it burned.

Woreta and her husband, both from Ethiopia, are alleging in a suit against GM that their car's destruction was directly related to the carburetor defect.