DUBLIN — Assemblywoman Catharine Baker unexpectedly secured a $20 million commitment from the governor’s office to pay for expanded parking at BART’s Dublin/Pleasanton station, which would fulfill a long-held promise by the transit agency to build a second garage there.

The only problem? BART’s governing board doesn’t want the garage. And that has the $20 million in limbo while Baker decides how to spend it.

Two people with knowledge of the deal claimed the money came in exchange for her vote on Gov. Jerry Brown’s cap-and-trade bill, but Baker, R-San Ramon, said it was just “an informal” verbal agreement with his administration because the garage would encourage people to take transit.

BART promised to build the 655-space parking garage back in 2002, when Dublin’s City Council approved a massive mixed-use development adjacent to the station. It was to be one of two garages there, with the first — a 1,528-space structure — completed in 2007. BART operates a total of 2,927 parking spots at Dublin/Pleasanton, all of which routinely fill up by 7:45 a.m., BART staff said in a report.

But the second project has long been delayed, mostly because of a lack of funds, said BART Director John McPartland, who represents the Dublin/Pleasanton district.

So, when staff came to the board in February with a $37.1 million proposal for a garage at the Dublin/Pleasanton station, many in the community rejoiced. But BART’s board balked at the price tag and unanimously sent staff back to the drawing board to come up with a cheaper scheme.

A revised plan presented in July cost roughly half as much — about $17.2 million — and would be faster to implement. It also would deliver the same amount of spaces through a combination of re-striping an existing surface parking lot, leasing spaces from nearby businesses with surplus parking and installing automated parking structures.

BART’s board was split on the new plan, voting 5-4 to adopt the so-called “hybrid” model, which also includes proposals to enhance the station’s connections to the Iron Horse Trail, install new bike parking and work with the local bus operator to improve transit to and from the station. The plan is more flexible, and would use attendant-assisted parking with automated parking structure modules added over time to test their effectiveness, staff said.

But Baker isn’t buying it. She doesn’t trust the automated parking structures, which are used worldwide but she said have yet to be tested at a transit station, where hundreds of people get off the train at the same time during rush-hour commutes.

“Look at how unreliable BART’s escalators and elevators are,” Baker said. “BART wants to promise that not only will that technology be reliable, but it will get them their car in 90 seconds. … I just don’t believe that plays out in reality.”

So where does that leave the $20 million? Baker says the money will be used to build some parking structure near the BART station, whether it’s on BART property or not.