U.S. efforts to make aging airliners safer could go into a stall for lack of repair capacity, the General Accounting Office said in a report it will present to Congress shortly.

The congressional investigative agency said federal regulations requiring stepped-up maintenance over the next four years may strain the industry's capacity. The report became available over the weekend.

"According to the airlines and repair stations we contacted, this increased demand for repair services may not be matched by corresponding increases in capacity in the immediate future," said the report.

The study was requested by the House Public Works and Transportation Committee's aviation panel, headed by Rep. James L. Oberstar (D-Minn.).

Recent safety regulations are likely to sharply increase demand for short-term repair services over the next four years, the study said. It said the changes could affect 1,400 of the 4,100 planes in the U.S. fleet.

Increased costs are expected to total $2 billion over the next four years. The amount is equal to all of the 1988 expenses to repair airframes. It would raise by about 9 percent the current $5.7 billion cost of repair and maintenance for U.S. airliners.

The report said the stepped-up maintenance is all but guaranteed to put a squeeze on repair capacity. It said some airlines then would have to ground airliners, ask for permission to delay repairs or fly them abroad for servicing.

The GAO surveyed five airlines -- Alaskan, American, Continental, Trans World and United -- which account for about 39 percent of the U.S. fleet. It also studied four independent repair stations, in Everett, Wash.; Santa Barbara, Calif.; San Antonio and Mojave, Calif.

According to the report, four of the five airlines expect to be operating near 100 percent of their hangar capacity this year.

It said, however, that three of the four independent repair facilities expect to have excess capacity totaling 5 to 19 percent this year.

But independents represent only about 20 percent of the industry, and that could mean excess repair capacity around 2 percent overall, the GAO said.

It added that even that slim margin could be squeezed. One repair station serviced 139 large transport craft in 1989 and turned away 153 others.