The General Accounting Office yesterday urged the Department of Transportation to reopen its investigation into an alleged Ford Motor Co. vehicle defect that is blamed for 250 deaths and several thousand injuries and is regarded by consumer groups as the most dangerous in the history of U.S. auto safety regulation.

However, the GAO also said that a new investigation of the supposed flaw -- the tendency of automatic transmissions on some vehicles to slip from park to reverse without warning -- might be too time-consuming to do much good.

As a "second option," the government, with or without Ford, should consider launching "a more extensive, long-term public awareness campaign" to warn drivers about potential park-to-reverse hazards and inform them about proper parking procedures, the GAO said in a report presented to Congress yesterday.

The alleged defect involves Ford cars and trucks manufactured for 1970 through 1979 model years. Nearly 20 million of these vehicles remain in operation.

The National Highway Traffic Safety Administration, a DOT agency, investigated the matter for three years, beginning in 1977. NHTSA formally closed the probe on May 4, 1981, four months after Ford agreed to send affected owners warning labels advising them that, under certain conditions, their vehicles could move from park to reverse inadvertently.

The labels were to be affixed to the dashboards of affected vehicles. But critics of the NHTSA-Ford settlement said it did nothing to reduce park-to-reverse deaths and injuries. Led by the Washington-based Center for Auto Safety and Rep. Timothy E. Wirth (D-Colo.), chairman of the House subcommittee on telecommunications, consumer protection and finance, the critics last year petitioned NHTSA to reopen its investigation.

NHTSA Administrator Diane K. Steed turned down that request last July. The GAO, Congress' investigative arm, yesterday agreed with Steed's contention that data and other information collected in the investigation of the case were often misleading. The agency also agreed with Ford's argument that "unexpected vehicle movement fatalities are not limited to Ford vehicles."

NHTSA officials had no immediate comment on the report yesterday. Ford said in a statement that it was "pleased by the GAO's fundamental conclusion that both Ford and NHTSA met their responsibilities" under the original settlement.