A Metrobus with no passengers aboard lost its brakes on upper Connecticut Avenue last night, precipitating a traffic-snarling chain of crashes that injured eight persons and damaged 10 cars and a lamppost, authorities reported.

All of the injured, including bus driver Karen L. Casey, were released from hospitals after treatment last night.

Northbound rush-hour traffic on Connecticut was backed up for more than an hour, with congestion extending south to the downtown area from the scene of the accident just south of The National Zoo.

The accident occurred at 5:15 p.m. when the bus, headed south toward Federal Triangle to pick up homebound rush-hour commuters, lost its brakes near Woodley Road, said Metro spokesman Al Long.

The bus struck the car in front of it, knocking the vehicle onto the Connecticut Avenue sidewalk, according to a police investigator. The bus then struck a second southbound car, knocking that auto into a third, which bounced back into the path of the bus as it was swerving to the left, police said.

Continuing to veer left, the bus struck a fourth car, which was thrown in turn against several cars parked on Woodley Road, police said. The bus also struck some or all of the parked cars before crunching to a halt against another car parked on Woodley.

"It was like a billiard ball effect," said one officer.

At some point in the sequence of skids, crashes and swerves, the lamppost and traffic light standard on the southeast corner of the intersection was toppled. It struck one of the parked cars. Total damage to the cars and the bus could not be immediately learned.

Casey, 28, a Metrobus driver for seven years, was taken to George Washington University Hospital where she was treated and released.

The seven other injured persons, all of whom had been occupants of the vehicles struck on Connecticut Avenue, were treated atGeorge Washington and at Georgetown University Hospital, and all had been released by 11 p.m.

Last night's accident appeared to be the first accident in several months involving brake failure on a Metrobus. Several incidents of failure had been reported in a brief period earlier this year. "We try our very best to send out a bus only if it's safe," said Metro spokesman Long.

Also contributing to this story was Washington Post news aide Ned Corrigan.