WASHINGTON (AP) _ Federal investigators will take a closer look at 1986-89 Hyundai Excels to seek the cause of engine fires that have prompted dozens of complaints, a government official said Tuesday.

The National Highway Traffic Safety Administration has received reports of 49 fires in the Korean-made cars, spokesman Tim Hurd said. An estimated 837,000 are on the road in the United States.

The agency opened a preliminary evaluation, involving mostly study and analysis on paper, in January. It decided last month to upgrade the investigation to what it calls an engineering analysis, in which actual parts are studied for defects.

Eventually, the agency could order the cars recalled for repairs.

Agency engineers believe the problem is linked to a pipe linking the air cleaner to the catalytic converter, Hurd said. When valves in the pipe malfunction, exhaust gases can ignite flammable materials around the air cleaner.

''Our engineers are working on the theory that that's what is happening,'' he said. No firm conclusion has been reached, he said.

''We don't believe there's any safety concern at this point,'' said Dotty Diemer, government relations manager for Hyundai Motor America, the U.S. subsidiary of Hyundai Motor Co. She said the company was preparing to respond to the agency's request for information.

In other cases, the agency said it had opened preliminary evaluations of:

-Loosing steering wheels in the Buck Regal, Oldsmobile Cutlass, Chevrolet Lumina and Pontiac Grand Prix models made since 1986. There has been only one complaint of a wheel coming unfastened.

-Gasoline leaks in 1987 models of the Chrysler Omni, Plymouth Horizon, Dodge Charger and Plymouth Turismo. There have been 17 complaints of leaks from a reservoir connected to the mechanical fuel pump. The pump has been replaced with an electrical pump on later models.

An estimated 288,800 of the cars are on the road.

-Failure of anti-lock brakes in 1988-1991 Ford light trucks. There have been 20 complaints blaming the problem for 14 accidents and seven injuries. About 1 million of the trucks are in service.

-Faulty headlights in the 1987-1988 Ford Mustang. There have been 13 complaints of the lights flickering when the fog lights are illuminated. An estimated 338,710 cars are on the road.

-Unexpected power surges in the 1991 Dodge Spirit and Plymouth Acclaim. Six complaints have been received, one alleging an accident, that the engine suddenly begins racing. An estimated 83,000 cars are in use.

Several preliminary evaluations were discontinued after no evidence of a widespread defect was found in examinations of:

-Unstable engine idling in the 1990 Volkswagen Jetta.

-Breaking door handles in the 1986-1988 Ford Taurus and Mercury Sable.

-Sliding door hinge failure in the 1990 Chevrolet Astro Van.

-A broken lug stud in the 1986-1989 Isuzu Trooper II.