BALTIMORE, DEC. 18 -- A federal jury has awarded $3.3 million to a 13-year-old Maryland youth paralyzed in a 1985 accident because the car in which he rode lacked shoulder harnesses in the rear seat and had only lap seat belts, the minimum requirement for U.S. cars.

The six-member civil jury found that both the lack of shoulder harnesses and what it said was defective design of the existing lap belts in the Ford Escort caused the injuries to the youth, Jimmy Garrett, of La Plata. The youth's back was broken in the Aug. 29, 1985, crash and he is now in a wheelchair.

The award -- one of the largest of the few such seat belt cases -- is considered significant among auto safety specialists, who say it could spur the federal government to require back-seat shoulder harnesses in American cars, currently an optional feature.

"This will send a message to Detroit," said Robert Dewey, spokesman for the Center for Auto Safety in Washington. " . . . It's urgent that auto manufacturers start putting {both} shoulder and lap restraints in the rear seats of car."

In a 1986 study, the National Transportation Safety Board recommended that automakers be required to install so-called lap-shoulder harness combinations in back seats, as they are in front seats now, but no action has been taken.

Ford Motor Co. says it has begun voluntarily phasing in rear-seat shoulder straps on some 1988 models.

A Ford spokesman in Detroit said today the auto giant will ask U.S. District Judge Joseph C. Howard in Baltimore to set aside the $3.3 million Garrett award or, failing that, appeal the case to the 4th U.S. Circuit Court of Appeals.

"While this case involved a tragic injury, we believe the jury completely ignored clear factual evidence showing there was no defect in the rear-seat restraint system and returned its verdict out of sympathy toward the plaintiff and his family," said spokesman Mike Moran.

The case stems from a midday accident in which the 1985 Ford Escort in which Jimmy Garrett was a rear-seat passenger collided with a tractor trailer truck on Rossback Road in Davidsonville in Anne Arundel County near where the Garretts lived at the time.

Garrett, then 11, suffered a broken back and massive internal injuries. His seat mate in the rear, Chris Gaboury, 13, was killed. Both were wearing lap belts, according to evidence in the trial. Seated in the front were the driver, Christina Kisamore, 17, who suffered a broken leg, and Karen Drumheller, 16, who suffered two broken legs. Police said Kisamore was wearing a seat belt and Drumheller was not.

According to Gerald I. Holtz, an attorney for the Garrett family, the impact caused Jimmy Garrett to undergo a "classic seat belt injury . . . . His upper body flexed over the belt, and it broke his back."

Also, because of improper design, Holtz said, the belt lay across his lower abdomen, rather than across his hips, causing extensive damage to his intestines from the impact of the crash.

The driver of the truck, Jackie Lee Hurd, escaped with minor injuries. Evidence indicated that the crash occurred when the Ford Escort crossed the center line of the road and hit the oncoming truck. Witnesses disagreed about the speeds of the vehicles. Ford attorneys argued that their combined speeds exceeded 50 miles per hour. Holtz and fellow attorneys Harold A. Sakayan and Solomon Margolis contended the speeds were much slower.

After an 18-day trial before Howard, the jury on Thursday found that Ford's failure to provide shoulder harnesses in the rear seat of the car -- even though they are optional under U.S. safety regulations -- "constituted a defect" and therefore caused Jimmy Garrett's injuries.

The jury awarded Jimmy and his father, Larry, a total of $3,311,345, representing past and future medical expenses, reduced income-earning ability by Jimmy and related pain and suffering. Jimmy, according to Holtz, at best, may be able to stand up "and take one or two steps" in the future.

There have been only a few similar "shoulder harness" lawsuits in the United States, with even fewer going to trial, as in the Garrett case. Several attorneys specializing in accident suits expressed surprise at the Garrett award because it appeared to require Ford to meet a higher safety standard than the lap belt requirement in order to avoid liability.

But Holtz noted that under U.S. safety laws, "compliance with any standard does not guarantee protection from liability."