The Transportation Department has notified Ford Motor Co. that the transmissions on 16 million Ford cars and light trucks contain a safety defect that permits them to slip accidentally from park into reverse.

If the interim determination by the National Highway Traffic Safety Administration is made final, it could lead to the largest auto recall in history.

Ford Automotive Safety Director Roger Maugh issued a statement later in the day saying the NHTSA conclusions "are based on faulty analysis and inaccurate and inadequate information."

The company denied there is a design defect in its transmissions and said Ford transmissions are basically the same as those installed in millions of other U.S., Japanese and European cars. "There's absolutely no reasonable or scientific basis" for NHTSA's conclusion, Maugh's statement said.

NHTSA will hold a public hearing July 21 to permit Ford and others to comment on the finding.

The interim finding ends a three-year-long investigation that NHTSA called its "highest priority."

NHTSA has received 23,000 complaints about the Ford transmissions, including reports of 6,000 accidents, 98 fatalities and 1,710 injuries allegedly attributable to transmissions slippage, a spokesman said.

The NHTSA finding covers Ford cars and trucks sold after August 1972 and before October 1979 with five types of Ford automatic transmissions, designated C-3, C-4, C-6, FMX and JATCO.

The investigation centered on 26 million Ford vehicles built since 1969, but an eight-year statute of limitations narrowed the notice to vehicles built after 1972. The transmissions were redesigned in 1980, NHTSA said.

The critical issue in the investigation was whether the transmissions contained a safety defect or whether, as Ford claimed, the accidents were due to the failure of motorists to put gearshift levers firmly in the park position.

NHTSA's interim finding describes two "apparent design errors" in the transmission. In some transmissions, internal spring forces can push the gear selection mechanism from park to reverse in certain circumstances, whether or not the gearshift lever has been pushed fully to the park position, NHTSA said.

In other transmissions, motorists feel they have shifted into park, when, in fact, the transmission is positioned between park and reverse, NHTSA said.

In either case, said NHTSA, the transmission can jump from park into reverse because of engine vibration or a jolt, such as the opening or closing of the car door.

Joan Claybrook, NHTSA administrator, said "owners should make sure their gearshift levers are shifted all the way to the park position, that the parking brake is set and that no vehicles ever be left unattended with the engine running."

According to NHTSA sources, the alleged defects may be remedied by installations of a special plate, at a cost of less than $20 per car. If a recall is ordered, Ford would face costs of several hundred million dollars.

The largest car recall to date occurred in 1971, when 6.7 million General Motors Corp. cars were cited for defective engine mounts.