The Transportation Department yesterday opened five separate investigations of possible safety defects in hatchback and tailback latches on a total of 2.6 million Mazdas, Subarus, Renaults, Toyotas, Pintos, Bobcats and Mustang IIs.

The National Highway Traffic Safety Administration said it first became concerned about the latches after a report from Spokane, Wash., that a child had been ejected through a hatchback door during an accident.

The agency added that its investigation has found 11 accidents resulting in two deaths and 14 injuries that were allegedly caused by latch mechanism failures in Ford Motor Co. cars.

In addition, NHTSA reported, four more latch-related accidents resulting in 11 injuries had been found involving Toyota vehicles.

Although the agency found no accidents involving the other vehicles, tests of those cars showed that the latches disengaged with even less effort than the Fords and Toyotas.

"Some manufacturers are apparently not using proper locking mechanisms," said NHTSA administrator Joan Claybrook. "Thus, people are being needlessly killed and injured."

Claybrook called on hatchback and station wagon owners to avoid driving with children riding in the rear compartments of their vehicles.

The investigations, which could lead to recalls, specifically involves 1975 Mazda RX3 station wagons, 1975 Subaru station wagons: 1976-79 type 1228 hatchbacks and station wagons; 1973-78 Toyota Corona station wagons; 1975-78 Toyota Corolla station wagons; 1971-78 Ford Pinto hatchbacks and station wagons; 1975-78 Ford Mercury Bobcat hatchbacks and station wagons, and 1974-78 Ford Mustang II hatchbacks.