A spokesman for the Federal Railroad Administration, which offered the project federal funding on the condition that construction begin in the Central Valley, said the agency will make no such stipulations about where the system should operate initially. Spokesman Mike Murray said that will be up to the rail authority board.

For its part, the Silicon Valley Leadership Group wants to see the northern section built before the southern route, even as it has taken no official position either way, said Jessica Zenk, senior director of transportation for the trade group.

"This is the hub for the innovation economy, the jobs that folks in the Central Valley want to be connected with. They're here," Zenk said. She added that the northern route would connect with Norman Y. Mineta San Jose International Airport much more directly than the southern option would link to Los Angeles International Airport.

Fill the gap

But state Sen. Alan Lowenthal, D-Long Beach, co-chairman of the Select Committee on High-Speed Rail, said it's more important to close the rail gap between Bakersfield and L.A. as a way of demonstrating the viability of bullet-train service as an alternative to driving or flying. He said the rail authority should consider doing this even before linking Bakersfield and Fresno.

"The object was not to connect the Central Valley to the Central Valley but to connect the Central Valley to the urban areas," he said.

At the same time, Lowenthal voiced support for the "blended" approach receiving greater attention lately. That option would cut costs by hooking up high-speed trains through the Central Valley with conventional commuter rail in the north and south. It also could spread out costs among different transit agencies.

This hybrid option has been advocated by the independent group Californians for High Speed Rail, which has taken no position on the northern versus southern options.

Executive Director Daniel Krause said the group would like to see a blended system linking the Central Valley to Palmdale while at the same time tying into a commuter rail station in Gilroy that connects to San Francisco.

Such a compromise would curtail the northern and southern options described in the rail authority's November business plan. Krause said construction could later continue either direction as more money becomes available.

"That would be ideal, where they kind of pursue north or south [initial operating segments] in a modified form," he said.

The rail authority board's vice chairman, Tom Richards, said some of these questions will be clarified in the revised business plan coming out within weeks.

But at an intuitive level, he said, the southern option may make more sense because it closes the Bakersfield-L.A. gap.

Considering that this option would open the system to the state's largest population center, "you say, 'Wow -- that certainly deserves attention,' " he said.