Silicon Valley boosters of California high-speed rail are jubilant at the revised plan to build the first stretch from San Jose to, um, somewhere north of Bakersfield instead of from Fresno to Burbank.

If this shift were a recognition of the importance of the valley economy to the state and to the success of an economically viable rail line, we’d be cheering, too. But it’s not. It’s an act of desperation. The High-Speed Rail Authority isn’t even pretending otherwise.

It says the change is because this stretch will be cheaper to build. The southern link will involve tunneling through mountains. Do the easier stretch first, is the theory, and then maybe the long-promised private investors in the system will actually materialize.

But guess what? Unless some Star Wars laser drilling technology is perfected by 2025, tunneling through mountains will not get any cheaper. The political resistance of Central Valley landowners won’t go away, either.

The idea really comes down to making the project too big to fail by building the easier part first and then saying: Really? We want this thing to end near (not even in) Bakersfield? No way.

But as the focus moves north again, controversy in this region will revive. Peninsula opponents, temporarily dormant, will be sharpening their litigious spears. And in San Jose, if cost concerns mean the rail line will come downtown on elevated tracks through popular neighborhoods instead of underground, the authority may get nostalgic for its Central Valley problems.

Even for the line to San Jose, the authority is counting on cap-and-trade money Gov. Jerry Brown sidetracked for the train. But that tax runs out in 2020. Brown will be gone by then, and at least one candidate to succeed him, Gavin Newsom, is not a high-speed rail fan. If President Barack Obama, a big supporter, is replaced by a Republican next year, forget federal dollars.

We supported the original $10 billion state bond for high-speed rail in 2008 and wanted the line to come through San Jose. We know big transit projects never have every dollar lined up before breaking ground — BART to San Jose didn’t — but if the cost is reasonable for the long-term gain, they’re worth supporting.

The cost estimate for the line in 2008 was $33 billion to go from Sacramento to San Diego by way of the Bay Area and Central Valley. At one point it hit $98 billion. Now it’s $68 billion, but the San Diego and Sacramento ends have been lopped off. The high cost of tickets may allow tech professionals to live in Madera, lucky them, and commute to Silicon Valley, but not the lower-income residents who suffer most from the cost of housing here.

The northward shift in plans and the reason for it now will set off a whole new round of controversy. Brace yourself.

And don’t put a down payment on that Madera mansion just yet.