Three months ago, Gov. Jerry Brown hit the reset button on the California bullet train, slashing $30 billion from its $98 billion budget and promising to reorder the controversial project's priorities.

Now, some Democrats in the state Senate want to hit the reset button again.

They have proposed dramatically shifting the high-speed rail project's focus by cutting back on planned construction in the San Joaquin Valley and instead spending billions on immediate rail improvements in Los Angeles and San Francisco.

It is not clear whether what lawmakers call "Plan B" -- a proposal devised by state Sen. Mark DeSaulnier, D-Concord, chairman of the Transportation and Housing Committee -- has a real chance of being substituted for the governor's proposal.

The issue will be settled soon, as the Legislature is expected to vote this week or next on whether to issue $6 billion in bullet train construction bonds.

The Senate Democrats' skepticism about the present high-speed rail plan was first reported by the Los Angeles Times.

Boosters say Plan B would spend money now to achieve high-impact upgrades of rail service in the state's busiest transportation corridors while building infrastructure that would accommodate bullet train service later on.

According to rail advocates who have been briefed on the idea, Plan B's top priorities include:

- A $2 billion tunnel through downtown San Francisco to bring commuter rail service -- and, eventually the bullet train -- into the city's new Transbay Transit Center from the Caltrain station more than a mile away.

- $1.5 billion in Los Angeles-area rail improvements, including a redesign of Los Angeles Union Station's rail access and construction of rail overpasses. Together, the projects would speed rail service for hundreds of Amtrak and Metrolink trains each day and end chronic traffic bottlenecks.

- A $1.5 billion San Joaquin Valley bullet train line between Fresno and Madera -- but with no immediate connections to Merced or Bakersfield.

In a statement, Dan Richard, chairman of the state High-Speed Rail Authority, asserted that Plan B couldn't be done.

"There are no legal, practical or contractual ways to move the money out of the Central Valley," he wrote. "The Authority's revised plan already makes major investments to rail across the state."

Californians for High Speed Rail, an organization that promotes the bullet train project, expressed alarm at the Plan B idea, warning that federal rail authorities might pull back $3.3 billion in promised project aid if the approach is pursued.

Construction of a 130-mile San Joaquin Valley segment is supposed to get under way as soon as the Legislature approves the sale of the bonds.

But some critics say the state has no idea where most of the construction money for the project will come from.