CALIFORNIA - BART and two of its three largest unions have agreed to extend their labor contracts through July 9 at midnight, and the president of a third union said she expected to sign a similar extension no later than this morning.

The agreements allow contract talks to continue and forestall the possibility of a strike that would shut down the transit system and displace the approximately 355,000 riders who depend on the system each weekday. BART's two other unions, both representing police, don't have the right to strike.

The contracts were extended beyond the previous June 30 deadline at the request of the state-appointed mediators who joined the talks Friday, according to BART spokesman Linton Johnson.

Union leaders welcomed the extension, saying that more time was needed to hammer out new contracts.

"We want to be part of the solution to help close the budget gap," said Lisa Isler, BART chapter president of the Service Employees International Union Local 1021, which represents about 1,450 mechanical and clerical workers. "We do not want to go on strike."

The two biggest unions - the SEIU and the Amalgamated Transit Union Local 1555, which represents almost 900 train operators and station agents - continued negotiating with BART Sunday, with the help of the four mediators, Johnson said.