The Biden administration will spend $1.2 billion to help build the nation’s first two commercial-scale plants to vacuum carbon dioxide pollution from the atmosphere, a nascent technology that some scientists say could be a breakthrough in the fight against global warming, but that others fear is an extravagant boondoggle.

Jennifer Granholm, the energy secretary, announced Friday that her agency would fund two pilot projects that would deploy the disputed technology, known as direct air capture.

Occidental Petroleum will build one of the plants in Kleberg County, Texas, and Battelle, a nonprofit research organization, will build the other in Calcasieu Parish on the Louisiana coast. The federal government and the companies will equally split the cost of building the facilities.

“These projects are going to help us prove out the potential of these next-generation technologies so that we can add them to our climate crisis fighting arsenal, and one of those technologies includes direct air capture, which is essentially giant vacuums that can suck decades of old carbon pollution straight out of the sky,” Ms. Granholm said on a telephone call with reporters on Thursday.

The 2021 bipartisan infrastructure law included $3.5 billion to fund the construction of four commercial-scale direct air capture plants. Friday’s announcement covered the first two.

Oil and gas companies lobbied for the direct air capture money to be included in the law, arguing that the world could continue to burn fossil fuels if it had a way to clean up their planet-warming pollution.

But many scientists are skeptical, and environmental advocates have criticized the approach.

In a TED Talk last month, former Vice President Al Gore gave a blistering critique of direct air capture technology, calling its use a “moral hazard” that would enable fossil fuel producers to continue to pollute.

“It’s useful to give them an excuse for not ever stopping oil,” he said. “That gives them a license to continue producing more and more oil and gas.”

Mr. Gore noted that the current cost of direct air capture technology was extraordinarily high and that the process required so much energy that it would make more sense to prevent carbon emissions in the first place rather than try to clean them up after the fact. Oil and gas companies say that the costs will fall and that the processes will improve in the coming years.

Currently, about 30 such plants have been commissioned worldwide, but Energy Department officials said that when the Texas and Louisiana projects were completed, they would be the two largest such facilities in the world.

The Energy Department projects that together the two plants will create 4,800 jobs and remove more than two million metric tons of carbon dioxide from the atmosphere each year, the equivalent of taking half a million gasoline-powered cars off the road.

Mitch Landrieu, President Biden’s infrastructure coordinator, called it “the largest investment in engineered carbon removal in history.”

The federal government’s push into such unconventional and expensive methods of carbon reduction comes on top of its central effort to fight climate change, which has been to offer $370 billion in tax incentives to bolster clean energy production and adoption of electric vehicles. That money was included in last year’s Inflation Reduction Act, the country’s landmark law to fight climate change.

But several analyses have shown that government subsidies will not be enough to meet Mr. Biden’s plan to cut the country’s greenhouse gas emissions in half by 2030 and to stop adding them to the atmosphere altogether by 2050. Those are the goals that scientists say polluting countries must achieve if the planet is to stave off the worst effects of climate change.

To achieve Mr. Biden’s goals, analysts say that the federal government and the states must use other tools, like tougher regulations, to cut emissions. That’s why some experts say that new technologies like direct air capture could be helpful.

“This summer’s horrible climate-related events, including today’s destruction of Maui, show the levels of greenhouse gas emissions are already too high,” said Michael Gerrard, an environmental law expert at Columbia University. “There is no scenario for meeting our climate goals that does not involve both the phaseout of fossil fuels and carbon dioxide removal on a massive scale. The technologies are still in their relatively early stage, but we’re going to need a lot of them, and we have to get going,”

To help new technologies get off the ground, the government is offering tax credits worth $180 for every ton of carbon pollution that is captured and stored by pumping it underground or into rocks, for example. Occidental and Battelle, in addition to being funded by the government, would be eligible for the tax credits.

Critics are concerned that the government’s foray into untested carbon capture technology could collapse, as it has before. The administrations of George W. Bush and Barack Obama poured over $1 billion into FutureGen, which was intended as a demonstration project to capture carbon and sequester it. The facility, a coal-fired power plant, was equipped with technology to extract and trap the greenhouse gases before they escaped from smokestacks. It was billed as a way to save the climate while still burning coal — but the project never demonstrated that the technology could be used at a commercial scale and was eventually shut down.

The lessons of FutureGen are at the forefront, said Kelly Cummins, the acting director of the Energy Department’s Office of Clean Energy Demonstrations.

“One of the things we’re trying to do is capture all the lessons learned from demonstration projects in the past, and incorporate then into oversight of this project,” she said. “We’re only approving one phase at a time, with a rigorous ‘go, no-go’ procedure. If any phase doesn’t work, it will be ‘no-go.’”