More than half of 711 trucks inspected by federal officials on a busy Pennsylvania highway recently were immediately ordered off the road because they were too poorly maintained to be safe, the Department of Transportation said yesterday.

Most of the 382 trucks that flunked the federal inspections had faulty or virtually inoperative braking systems, federalo officials said.

"I am really surprised at the high rate of failure," said W. R. Fiste, of the Bureau of Motor Carrier Safety, which conducted the inspections with a team pulled from several regional offices. "This is the highest failure rate we have ever encountered."

For a truck to be ordered off the road, it had to have a maintenance problem that made it "imminently hazardous." Fiste said. Brake problems on 286 trucks included leaky air lines, some disconnected brake drums and improperly maintained hoses.

Forty trucks were removed from the road for inoperative lights, 25 for bad suspension systems and 21 for tire problems.

Additionally, 24 drivers were found to be violating the federal regulation that limits their time behind the wheel.

The bureau's inspection was conducted on Interstate Rte. 80 near Berwyck, Pa., between Aug. 7 and 11. All vehicles were stopped, so there was no possibility of ignoring the checkpoint.

Inspectors made a cursory check of every truck, then singled out the 711 for intensive inspection. Normally, Fiste said, 25 to 30 percent of the selected trucks would be placed out of service because of maintenance defects. Why was it so much higher on this check?

"We don't really know," he said. "But we were working in virgin territory as far as this kind of inspection is concerned."

The bureau started its unannounced intensive inspections last September. It has been under considerable pressure from Congress to beef up truck inspections, but says it has only 133 inspectors nationwide for 5 million trucks. Twenty-six more inspectors are included in the new budget proposals.

Of the 382 trucks that were ordered off the road. 215 were owned and operated by Interstate Commerce Commission-authorized carriers. The rest were independent operators.

A spokesman for the American Trucking Associations termed the results of the Berwyck inspections "not reassuring." "We're in favor of more enforcement," he said. "We think it's the only way. They should certainly have more inspectors."