For the last week — since a 60-day cooling off period ordered by Gov. Jerry Brown ended on Oct. 10 — negotiators for BART and the transit workers’ two largest unions had been working long hours trying to resolve their differences. But late Thursday afternoon, union leaders and BART managers, their frustration evident, emerged bleary-eyed from 28 straight hours of negotiation to say they had failed to reach a deal. George H. Cohen, head of the federal mediation service who flew in on Monday, said there was nothing more that mediators could do.

“I’m surprised and sorry to be standing here tonight,” Pete Castelli, executive director of the Service Employees International Union 1021, said Thursday evening. “In all my years in the labor movement, I’ve never seen an employer drive negotiations that were this close to a deal into a strike.”

The service employees’ union and the Amalgamated Transit Union Local 1555 together represent 2,400 train operators, station agents, mechanics, clerical workers and other employees of the transit system. Mr. Castelli and other union representatives said the unions had compromised on pensions and health care and were close to an agreement on wages. But the talks broke down, they said, over how to handle disputes over work rules, including shift lengths and overtime. An offer to refer those issues to an arbitrator whose decision would be binding was turned down by management, the union leaders said.