Driven by the difficulty of meeting clean energy goals and by surging electricity demands, a growing number of political leaders are taking a fresh look at nuclear power — both extending the life of existing reactors and building new ones.

Even past skeptics, largely Democrats, have come around to the idea — notably in California, where the state’s sole remaining nuclear plant, Diablo Canyon, is scheduled to close in 2025. The search for clean energy has given nuclear power a spark that has drawn bipartisan support that added billions in funding for existing and new projects.

But critics of the nuclear industry argue that a veneer of clean energy has not changed the concerns about the technology, including aging facilities in need of potentially costly improvements, the challenge of nuclear waste disposal and steep cost overruns for new projects that are years late — if they reach completion.

“The industry knows it does not have a good story to tell,” said Edwin Lyman, a physicist and the director of nuclear power safety with the Union of Concerned Scientists. “It’s still plagued by the same issues.”

President Biden wants to eliminate greenhouse gas emissions from the power industry by 2035, and he said a Supreme Court ruling last week limiting federal regulatory authority would not halt such efforts. But the supply chain issues that have hurt wind and solar power development have presented the latest hurdle to reaching that goal.

As a stopgap, the Biden administration has established a $6 billion fund to help troubled nuclear plant operators keep their reactors running and make them more economically competitive against cheaper resources like solar and wind power. The application deadline is Tuesday, though it might be extended and the requirements amended to broaden eligibility.

“The Biden administration has been very clear that we will get to the net zero goals,” Kathryn Huff, assistant secretary for nuclear energy at the Department of Energy, said at a recent conference of the American Nuclear Society. “They’re incredibly aggressive goals, and nuclear is a part of that solution, a very big part potentially.”

In addition to the $6 billion fund, the administration is providing $2.5 billion for two projects meant to demonstrate new nuclear technology, in Washington State and Wyoming.

A separate bipartisan measure introduced last year is aimed at preserving and expanding nuclear energy in the United States. The bill, whose backers include Senators Shelley Moore Capito, Republican of West Virginia, and Cory Booker, Democrat of New Jersey, would provide financial assistance like tax credits, according to the Tax Foundation, a nonprofit tax policy organization.

Ms. Capito has argued that coal-fired power plants, which have been closing as the nation moves away from fossil fuel sources, could become sites for nuclear reactors. That would provide benefits for places like her home state, which has produced coal and relied on it as fuel for power generators.

“Ultimately, you get to a point where you need something that’s not weather dependent, something like nuclear to make the grid reliable,” said John Kotek, who ran the Office of Nuclear Energy during the Obama administration and is now vice president for policy at the Nuclear Energy Institute, a trade association. “There are other technologies that are candidates to play that role, but if you look at what is available today across the widest scale, that’s nuclear energy.”

The rising costs of other sources of power have made nuclear energy more competitive around the world, including in the United States, which has the largest fleet of nuclear plants of any country. They produce about 20 percent of the nation’s electricity and 50 percent of the clean energy.

The United States maintains 92 reactors, though a dozen have closed over the last decade — including, a month ago, the Palisades Nuclear Generating Station in Michigan, about 55 miles southwest of Grand Rapids.

The owner, Entergy, decided to shut the plant after a power-purchase agreement with a utility expired. Entergy said it could not find buyers for the plant, and decommissioning has gone too far to bring it back online, even with the money from the federal government.

Diablo Canyon is next on the decommissioning list, but Gov. Gavin Newsom has proposed extending its life. The plant, on California’s central coast, supplies almost 10 percent of the state’s electricity. Pacific Gas & Electric, which owns the plant, announced in 2016 that it planned to close it when its licenses expired, saying it would focus more on solar and wind power as renewable energy sources.