LOS ANGELES (AP) — California is about to send the nation a powerful message on the future of nuclear power — it’s just not clear what it is yet.

Legislators in Sacramento are expected to vote this week on Democratic Gov. Gavin Newsom’s proposal to extend the life of the Diablo Canyon Power Plant by up to five years, which he says is needed to ward off blackouts and advance clean-energy goals amid a warming climate.

The complex plan has set off a furious lobbying war between environmentalists and industry-linked groups at a time when the long-struggling nuclear energy sector foresees a rebound for its carbon-free power in the age of climate change. It would erase an earlier agreement to close the state’s last operating nuclear plant by 2025.

If approved, the extended lifespan for Diablo Canyon would carry symbolic weight in the birthplace of the modern environmental movement, and signal that nuclear power is being embraced as part of a strategy to keep the lights on and rising temperatures in check, despite the highly radioactive waste it leaves behind.

“California will need Diablo Canyon and every other clean energy resource it has to meet its electric reliability, environmental and climate goals,” the American Nuclear Society said in a letter to legislators this week, urging a longer run for the reactors.

Friends of the Earth, an environmental group that was part of the 2016 agreement to shutter the plant, kicked off a digital advertising campaign Tuesday in an attempt to sway undecided legislators and build public support to block an extension.

Newsom’s “decision to try and extend the life of Diablo Canyon is reckless beyond belief,” the group’s president, Erich Pica, said in a statement.

There have been competing studies about whether extending operation of the decades-old reactors would gouge ratepayers, or be a bargain. The plant is located within a web of earthquake faults, and the prospect of a longer lifespan has reignited long-running disputes over seismic safety that have shadowed the plant since construction began in the 1960s.

A last-minute push from both sides included a letter to legislators from Democratic U.S. Sen. Dianne Feinstein, reiterating her support for an extended run. The Environmental Working Group, a nonprofit advocacy organization that opposes the extension, warned Tuesday that the bill would hit residential solar customers with a monthly tax for electricity they generate and use to power their homes.

It was unclear which way the vote would break. Newsom expressed confidence he would prevail during a recent visit to Los Angeles.

He said he saw the Diablo Canyon extension as part of a much larger transition away from fossil fuels as the state reckons with climate change. The plant “in the short run needs to be part of that transition,” he said.

To pass, the proposal needs a two-thirds vote in the state Assembly and Senate, a threshold that can be difficult to reach. Meanwhile, a group of Democratic legislators unveiled a rival plan that would speed up development of renewable power and transmission lines, while leaving intact plans to shutter the plant located midway between Los Angeles and San Francisco by 2025.

Lawmakers have questioned why Newsom dropped the text of his legislation just days before the end of the Legislature’s two-year session on Wednesday, saying it provided virtually no time to carefully review it.

Daniel Hirsch, retired director of the program on environmental and nuclear policy at the University of California, Santa Cruz and a longtime critic of nuclear plant safety, asserted during an online news conference that Newsom introduced the proposal at the end of the legislative session to avoid scrutiny.

The bill with vast consequences is being “jammed through,” he said.

Even if the governor's plan advances, many questions remain.

If it is approved, plant operator Pacific Gas & Electric plans to seek a share of $6 billion the Biden administration has set aside to rescue nuclear plants at risk of closing. But if the money doesn't come through, the state could consider backing out of the deal.

The plant began running in the mid-1980s, and it isn't known what the cost of deferred maintenance will be, given that PG&E was preparing to close the plant. PG&E also would need approval to keep running from the Nuclear Regulatory Commission, a process that has not started and sometimes takes years to complete.

Issues from the safe storage of spent nuclear fuel to adequately staffing the plant for a potentially longer run are also in the mix.

President Joe Biden has embraced nuclear power generation as part of his strategy to halve greenhouse gas emissions by 2030, compared to 2005 levels.

"A clean, affordable, and reliable grid requires a strong backbone ... like Diablo Canyon,” the nuclear society letter said.