Representatives from Amalgamated Transit Union Local 1555 and Bay Area Rapid Transit negotiated through the weekend in a last-ditch effort to avoid a walkout affecting some 330,000 riders who use the nation's fifth largest rail system on weekdays. The pact still must be ratified by BART's 900 operators and ticket agents.

"We've worked to an agreement that we believe is equitable," union president Jesse Hunt said. "We're pleased to announce this tentative agreement. Our members will be working tomorrow. Trains will run."

Hunt said the agreement calls for a four-year contract, but he would not discuss details. He said he was confident his members would approve the deal in a vote next week.

While both sides reported progress in talks throughout the weekend, San Francisco Mayor Gavin Newsom and BART vice president James Fang told reporters there was a tentative deal several hours before the strike was to start at 12:01 a.m. Monday.

"It puts us in a position where people are able to get to work tomorrow," said Newsom.

Transportation agencies in the region were preparing to increase service in the event a BART strike would overwhelm the area's freeways and public transit services.

"I'm happy it's resolved, but we had contingency plans in place, just in case," said Randell Iwasaki, director of the California Department of Transportation.

Facing a $310 million deficit over the next four years, BART is seeking $100 million in labor cost savings, including $38 million from Local 1555. The union announced that its members would strike Monday after BART's board of directors imposed work terms that the union says amount to a 7 percent pay cut.

Experts said a BART strike had the potential to severely disrupt the area's busy freeways and batter its already-bruised economy. BART board member Lynette Sweet said it would have cost the agency more than $1 million a day.

The strike reprieve was welcomed by BART riders.

Rider Robert Pierce, 39, of Oakland said he was glad it was averted. He said the thought of a strike in this economy made him "mildly furious."

A strike also would have compounded a tumultuous year for BART, which has come under scrutiny after a fatal shooting of an unarmed passenger by a BART police officer on New Year's Day and a publicly criticized fare increase.

A strike could have put another 60,000 vehicles on the road and created hours-long delays on roadways, the Metropolitan Transportation Commission said. Officials had encouraged commuters to leave an hour or two early and to use possible alternatives such as car pools, arriving and leaving work later and working from home.

BART had planned to provide limited bus service between stations in the East Bay and downtown San Francisco. Other transit agencies planned to expand ferry service from Oakland and Alameda County to San Francisco, as well as bus and streetcar service in San Francisco.

Lauren Wonder, spokeswoman for the state transportation department, said late Sunday contingency plans will not be carried out. "It won't be the commuter challenge had there been a strike," said Wonder.

The agreement's four-year contract is similiar to one accepted by two other BART unions. The operators and station agents earlier rejected a four-year contract and their union was seeking a shorter contract.

"With this agreement, the hundreds of thousands of Californians that rely on the services BART provides will be able to continue to conduct their everday business without interruption," Governor Arnold Schwarzenegger said.

BART board president Thomas Blalock said discussions Saturday were focused on how to draw an acceptable four-year contract that would meet BART's target for cost savings. Blalock said the disagreements revolved around work rules rather than salary and benefits.

Sweet said that as talks resumed on Saturday it looked as though neither side was going to blink, but movement toward a deal came Sunday afternoon.

"Yesterday it looked dire, today it appeared better and tomorrow we'll be up and running," Sweet said.