OpenAI is close to leasing a $500 billion data center in southern Ohio that could be among the largest of the artificial intelligence boom, according to three people familiar with the project.

OpenAI is in separate talks with the chipmaking giant Nvidia for a $250 billion financial backstop for the project, said the three people, who spoke on the condition of anonymity because they were not authorized to discuss it.

The U.S. government, which is helping to provide the electrical power for the project, is still talking to other potential tenants, and the deal will not be final until Commerce Secretary Howard Lutnick agrees to it, one of the people said.

But the Japanese conglomerate SoftBank, an OpenAI investor that is leading the development of the data center, and government officials are leaning toward OpenAI as the main tenant because Nvidia has added financial muscle to the A.I. company’s proposal, the three people said.

Microsoft, Google and possibly other companies have also submitted bids to use the data center, the people said. The center, financed in part through a trade deal with Japan, will be backed by 10 gigawatts of electricity, which is enough to power millions of households.

The financing for the Ohio project is indicative of the elaborate deals that have helped fuel the A.I. boom over the past several years. Through unusual and creative arrangements with chipmakers, cloud-computing companies and governments across the globe, start-ups like OpenAI and Anthropic are tapping into huge amounts of computing power they could not afford on their own.

Many of these deals can be described as circular. A start-up will receive billions of dollars from giant tech companies before sending those billions back to the same companies to pay for computing power and other services.

Last week, Anthropic announced such deal with AMD, one of Nvidia’s chief rivals. AMD agreed to invest $5 billion in Anthropic, while Anthropic agreed to buy tens of billions of dollars in hardware from the chipmaker. OpenAI has made similar agreements with AMD, Nvidia and others.

Nvidia would allow OpenAI and its partners to receive more favorable terms on the billions of dollars in debt they must raise to help fund the project. Nvidia would agree to cover both OpenAI’s lease payments and its debts if the start-up was unable make payments on its own.

Nvidia, with a market valuation of nearly $5 trillion, is one of the few companies in the world that have the financial wherewithal to backstop a deal of this size. It can help a smaller company raise large amounts of money at reasonable interest rates.

That makes the deal less risky, said Jeremy Kress, an associate professor of business law at the University of Michigan who specializes in financial stability and systemic risk in the economy.

“It is nice to have a backstop,” he said. “You want to see stable money that can absorb loses.”

The Wall Street Journal reported earlier on the talks between OpenAI and Nvidia.

From 2019 through 2023, Microsoft pumped more than $13 billion into OpenAI. Then OpenAI funneled most of those billions back into Microsoft, buying cloud-computing power needed to fuel the development of new A.I. technologies. Anthropic made similar agreements with Google and Amazon. And Google has provided chips and financial backstops for new data centers built by Anthropic and other partners.

(The New York Times has sued OpenAI and Microsoft, claiming copyright infringement of news content related to A.I. systems. The two companies have denied the suit’s claims.)

OpenAI’s latest effort is even larger and more elaborate. Nvidia, which previously invested $30 billion in OpenAI, is also considering financing the purchase of $350 billion of its chips for the data center in Ohio, a person familiar with the talks said.

The U.S. government is providing the electrical power through a partnership with Japan. The Japanese government agreed to help fund the project as part of an agreement to invest in U.S. projects in exchange for lower tariffs. Mr. Lutnick will need the approval of the Japanese government to complete the deal.

SoftBank, a longtime investor and partner of OpenAI, is building the data center from a decommissioned Cold War-era uranium enrichment plant on federal land in Piketon, about 50 miles south of Columbus. The project is still in the early stages, and it is not yet clear when the data center will be completed. The first stage of construction is planned for completion in 2028.

Financial experts have long warned that such deals pose risks to the economy because companies are taking on enormous amount of debt to fund new data centers — and because of the circular nature of many of the deals.

“Five hundred billion dollars is a very large project, even given the current level of spending across the industry,” said Gil Luria, head of technology research at the investment firm D.A. Davidson. “Is this investment worthwhile? Will it generate the appropriate returns? Is it sustainable? This is the right conversation to have.”

Dr. Kress said that even if Nvidia was backstopping the deal, it still would come with risk. If OpenAI struggles to repay its debts, that may mean that the entire A.I. industry, including Nvidia, is in financial distress.

“It is not really outside equity that it coming in to backstop the project,” he said. “There is a very high correlation between Nvidia’s business and the success of this project.”

Mr. Luria said some investors were already beginning to see sizable returns from their data center deals. This includes tech giants like Google as well as investment banks like Blackstone.

Google said last week that its revenues in the three months that ended in June rose 24 percent from the previous year, boosted by the company’s investments in A.I.-related companies like SpaceX and Anthropic. Gains tied to those investments were valued at about $99 billion and contributed $77 billion to the company’s overall profit.

When Blackstone reported quarterly earnings last week, Stephen Schwarzman, the company’s chief executive, said the “most significant driver” of its results had been investments in A.I., specifically citing data centers, energy and power as well as A.I. companies.

“We are in the early days of what I believe will be the most consequential transformation in industry and markets in a generation,” Mr. Schwarzman said during the firm’s investor call.