The National Highway Traffic Safety Administration is expanding its probe of sudden acceleration in passenger cars, the agency has informed a Washington-based consumer action group.

The agency investigation, which includes a series of General Motors Corp. and Audi cars, is being broadened to include 3.2 million Ford Motor Co. cars manufactured for the 1983 through the 1986 model years, according to a June 1 letter by NHTSA enforcement director George L. Parker.

The Ford cars in question had been under investigation for the alleged defect. But the investigation was closed because the agency could find no defect trend in the Ford cars, Parker said in his letter to the Center for Auto Safety. The center last November petitioned NHTSA to reopen the Ford probe.

"Sudden" or "unintended" acceleration sometimes occurs in automatic transmission cars when drivers shift from park to the reverse or drive gears. The car moves forward or backward with seemingly uncontrollable speed, possibly causing loss of driver control over the vehicle. NHTSA in the past 15 years has conducted more than 50 investigations of sudden acceleration involving more than 20 auto makers.

Some of the sudden-acceleration investigations "concluded with voluntary or ordered recalls for easily detected defects in cruise control systems or throttle assemblies," according to a report published this month by the McLean-based National Automobile Dealers Association.

But most of the investigations "were dropped when no mechanical or design defect trend was found," the NADA report said.

Parker said new evidence presented by CFAS "identifies a possible defect trend" in the cited Ford cars "involving engine surge under circumstances that may compromise vehicle controllability."

Ford officials in Dearborn, Mich., yesterday told United Press International that they could see no reason for NHTSA's reopening the investigation and expressed confidence that their vehicles do not have an acceleration problem.

The Ford cars in question include the Crown Victoria, Ford LTD, Mustang and Thunderbird; and the Lincoln/Mercury Grand Marquis, Marguis, Cougar, Colony Park, Continental and Mark VI and VII.