SAN FRANCISCO (Reuters) - A judge on Sunday blocked a threatened San Francisco-area rail worker strike that could have disabled a critical part of the region's transportation system serving 400,000 daily passengers.

The ruling by San Francisco Superior Court Judge Curtis Karnow to bar Bay Area Rapid Transit District workers from striking took effect immediately and remains in place through October 10, 2013. It provides a cooling-off period in the contentious labor negotiations.

BART management and the unions representing its 2,600 workers have been in talks for more than four months and have been millions of dollars apart on a potential settlement.

The judge issued the injunction following a rare Sunday-morning hearing, which he said was held to determine whether a strike would "significantly disrupt public transportation services and endanger the public's health, safety or welfare."

"This hearing has nothing at all to do with the merits of this dispute between the unions and BART," Karnow said.

Neither BART management nor the unions objected to the injunction in court.

California Governor Jerry Brown sought the 60-day injunction on Friday.

The strike would have been the unions' second walkout of the summer.

The BART rail system was shut down for 4-1/2 days in July when union workers walked off the job, creating severe roadway congestion and forcing commuters to miss work or crowd onto a limited number of other public transportation options.

Brown averted a proposed strike last Sunday by appointing a three-person board to investigate the BART labor feud. The board was charged with hearing from both sides and reporting back to the governor on its findings.

After a heated public meeting on Wednesday, the board found that a strike would result in "significant harm to the public's health, safety and welfare," Brown said on Friday.

The public safety threat determination was needed for Brown to seek the cooling-off order.

BART management, which had supported the cooling-off time, reported a $62 million gap in contract terms at Wednesday's meeting.

Union officials, who had opposed the cooling-off period, said there was a $56 million difference in proposals.

Management has said it offered workers a 9 percent pay raise over four years but wants employees to pay 5 percent of their salaries toward pensions. Employees currently do not contribute to their pensions.

The unions have said they want a 15 percent raise over three years and that additional pay increases would be needed to offset the higher benefit contributions.

BART management says the average employee gets an annual salary of $79,500 plus $50,800 in benefits, and it is concerned the cost of benefits will continue to climb after increasing by nearly 200 percent in 10 years.

Union representatives peg salaries of BART workers at $64,000 on average, saying that management's figures included higher salaries for managers.

(By Laila Kearney. Editing by Kevin Gray, Ellen Wulfhorst, Jackie Frank and Cynthia Osterman)

[El Cerrito Del Norte BART Station via Wikipedia Commons]