Faced with a shortage of money and political support after seven years of work, Gov. Jerry Brown’s administration is working on a plan to scale back one of his key legacy projects — a $17 billion proposal to build two massive tunnels under the Sacramento-San Joaquin River Delta to make it easier to move water from Northern California to the south.

Instead of two tunnels, each 40 feet high and 35 miles long, Brown’s Department of Water Resources has been negotiating with major California water agencies in recent weeks on a revised plan to build just one tunnel at slightly more than half the cost of the original project.

The new plan reflects the reality that Brown has only one year remaining in office and that the original project has failed to win enough financial backing from water agencies around California that Brown was asking to pay for construction.

The new approach — a huge shift in the often-intractable world of California’s water politics that has implications on everything from the environment to the water bills of millions of people — could be announced within the next month, said Jeffrey Kightlinger, general manager of the influential Metropolitan Water District of Southern California, which serves 19 million people in Los Angeles, San Diego and other areas.

“I’m hopeful this will be seen as a kinder, gentler, more agreeable approach,” Kightlinger said.

The two tunnels would have a capacity of 9,000 cubic feet per second, which is about 4 million gallons per minute. But the one tunnel would carry from 3,000 to 6,000 cubic feet per second, Kightlinger said.

The two-tunnel project could still be saved in its current form, Kightlinger said. But he conceded that it is increasingly unlikely, given the fact that major players such as Westlands Water District in Fresno and the Santa Clara Valley Water District in San Jose voted in recent months not to fund it. But in negotiations over whether to have one or two tunnels, it became clear that there are nearly enough commitments from water agencies to get close to funding a one-tunnel project, he said.

“Unless we can figure out the money in the next 30 days, which seems really difficult, my hunch is we’re heading toward the latter,” he said. “You need about $10 billion to get to the single-barrel approach. I think we’re pretty close to having that.

Kightlinger said the project could be built in phases, with a second tunnel an option but with no timetable for construction. “Whether or not that ever happens, who knows,” he said.

Environmental groups have fought the twin tunnels plan and vowed to tie it up in court over concerns that the project could result in large San Joaquin Valley farms and Southern California cities potentially taking more water in the future from Northern California, harming the Delta’s fragile ecosystem. But in 2013, several environmental groups, including the Natural Resources Defense Council, Planning and Conservation League, Defenders of Wildlife and the Bay Institute called for the state and federal government to study a one-tunnel project that would carry 3,000 cubic feet per second. The groups said the tunnel could potentially move significant amounts of water south in wet years, reducing the need to pump during dry years when salmon, smelt and other fish species are most at risk.

On Friday, the groups said they needed to hear more details.

“We’ve always wanted to study a smaller facility,” said Doug Obegi, an attorney with the Natural Resources Defense Council in San Francisco. “But the state and feds refused to study it. And it’s pretty ironic that they seem to be pivoting to a smaller project now.”

Obegi said the primary goal of his organization is to get the state to take less water from the Delta. Regional projects like water recycling, stormwater capture and the construction of new off-stream reservoirs should instead meet California’s future water needs, he said. Other environmentalists agreed, saying want more details of how much water would be taken in a single tunnel, when and what the impacts on the environment would be.

“After spending over a quarter of a billion dollars pushing for the big tunnels, the state and the Metropolitan Water District have finally recognized that it is dead,” said Jonas Minton, a senior water analyst with the Planning and Conservation League. “The problem with a somewhat smaller version is that it still lacks all the safeguards required to ensure that it will not destroy the environment and economy of the Bay Delta estuary.”

The water agencies involved in the negotiations include Metropolitan, the Santa Clara Valley Water District, the Kern County Water Agency and other contractors of the State Water Project.

“Let’s try it in a smaller size, and if it works the people will have confidence in it,” said Dick Santos, chairman of the Santa Clara Valley Water District board. “I think that is a fair compromise.”

A report released in October by State Auditor Elaine Howle noted that the state originally said the tunnels project would cost $140 million to study and permit, but that so far local water agencies have spent $280 million. The state “has not completed either an economic or financial analysis to demonstrate the financial viability” of the project, which the Brown administration calls the California WaterFix, Howle said.

John Laird, secretary of California’s Natural Resources Agency, said he could not discuss details of the negotiations between the state Department of Water Resources and other large water agencies. But he did not dispute Kightlinger’s characterization of the talks.

“We are in negotiations,” Laird said. “We hope they are concluded in the next few weeks. Everything is on the table and we hope to get a project that can be built.”

The Delta tunnels plan was launched under former Gov. Arnold Schwarzenegger. The idea is that the tunnels would take water from the Sacramento River, south of Sacramento near the town of Courtland, and move it to the huge pumps near Tracy that are part of the State Water Project and federal Central Valley Project. That, supporters say, would reduce reliance on the pumps and make water deliveries more reliable by protecting endangered salmon, smelt and other fish, which can be killed by the pumps.

But critics called the proposed twin tunnels a boondoggle that would eventually allow large agribusiness interests in the San Joaquin Valley, as well as urban users in Los Angeles, to take more water out of the Delta, regardless of what promises are made now.

Complicating Brown’s plans, his administration has not been able to guarantee that the tunnels will allow any more water to be pumped out of the Delta than is being pumped out now — roughly 50 percent of all its fresh water in most years.

Meanwhile, political intrigue is swirling. Earlier this week, Grant Davis, who was named executive director of the state Department of Water Resources in July, resigned abruptly to take back his former job as general manager of the Sonoma County Water Agency.

Davis, a former environmental activist with the Bay Institute, was replaced by Karla Nemeth, who has worked in the Schwarzenegger and Brown administrations since 2009, largely on the Delta tunnels project. Nemeth is married to Tom Philp, a chief strategist at the Metropolitan Water District.