SACRAMENTO — Gov. Jerry Brown is considering scaling back his controversial twin-tunnels plan to move water around the state, from two tunnels under the Sacramento-San Joaquin River Delta to one.

In a Department of Water Resources memo sent Friday to potential contractors, state officials for the first time indicated that they are considering a single-tunnel plan. The memo also says the Department of Water Resources “is in the process of evaluating” other possible changes to the tunnels project, including constructing the project in stages.

Although no decision has been made on whether to scale back the $17 billion project that Brown has championed for years, the water resources department sent the memo so that interested contractors could determine how such changes would affect their bids, Lisa Lien-Mager, a spokeswoman for the California Natural Resources Agency, which oversees the department, said in a statement Tuesday.

“The project has not changed,” Lien-Mager said.

Brown’s plan to build two tunnels under the Delta has faced significant financial obstacles and opposition from environmental groups.

The proposal envisions two 35-mile tunnels that would move water from Northern California to farms and cities to the south, including in the Bay Area. Supporters have argued that the Delta’s existing water infrastructure is outdated and distributes too little water to the Bay Area, the Central Valley and Southern California.

The tunnels would bypass that aging system of canals.

Brown has argued that the project has had “more environmental review than any other project in the history of the world.”

“It is absolutely essential if California is to maintain a reliable water supply,” Brown said in December 2016 after the final environmental impact report was released.

The supporters of California WaterFix, as the tunnels project is called, say the diverted water from the Delta would deliver more water around the state without harming dwindling fish populations.

Opponents include many environmental groups and Delta farmers who worry about the tunnels’ effects on the Delta’s fragile ecosystem. While some — including the Natural Resources Defense Council — have argued for a single tunnel, they also want to reduce overall water diversions from the Delta.

It’s unclear whether a single-tunnel alternative would achieve this because details have yet to be released.

“I’m very skeptical, unfortunately,” said Doug Obegi, an attorney at the Natural Resources Defense Council. “It is clear the larger project was economically infeasible. They didn’t have the money for it. My fear is that although they appear to be downsizing the project, they are likely to divert as much water or more from the estuary — and that’s not consistent with what is needed to restore and protect the health of the Delta.”

The twin-tunnel project hit a financing snag in September when Westlands Water District, a politically powerful San Joaquin Valley supplier, voted against paying 20 percent of the price.

With Brown in his final year as governor, his office began talks with other water agencies in recent weeks about a single-tunnel plan in hopes of garnering support. The Santa Clara Valley Water District voted in October to conditionally support the project if it becomes one tunnel. Santa Clara County receives 40 percent of its water from the Delta.

Support from the Santa Clara water district was seen as critical to push back against opponents who have characterized the project as a water grab by Southern California cities and corporate farmers.

Richard Santos, the water district’s board chair, said the agency continues to work with the state on the Delta proposal and that the board could vote on any changes announced by the state in the spring.

“We’re optimistic that the state will be able to present a project that meets the principles we approved in October,” Santos said in a statement.

State water officials said construction could still begin later this year.

Melody Gutierrez is a San Francisco Chronicle staff writer. Email: mgutierrez@sfchronicle.com Twitter: @MelodyGutierrez