The chief executive of U.S. Steel said on Tuesday that the proposed takeover of the company by Nippon Steel of Japan would strengthen America’s national security, and he expressed confidence that the federal government would allow the deal to close despite bipartisan calls to block it.

Rebutting concerns from lawmakers and the steelworkers’ labor union about the transaction, the executive, David Burritt, argued that if the acquisition moved forward, the new company would benefit the U.S. economy and allow the United States and Japan to better compete with China in global steel markets.

“By the time we’re done doing all the analysis, it’s very clear that it strengthens national security, economic security and job security,” Mr. Burritt said. “This deal will close on its merits.”

His comments, made at the Detroit Economic Club, came as U.S. Steel has been facing a political storm over Nippon’s $15 billion takeover bid. Top Republicans and Democrats, including President Biden, Vice President Kamala Harris and former President Donald J. Trump, have said that the iconic steel maker should remain American owned and operated. The United Steelworkers union has accused Mr. Burritt of misleading workers and trying to get a lucrative exit package that would come from selling the company.

The transaction has also become tangled with swing state politics, as U.S. Steel is based in Pennsylvania, which could help to determine the outcome of the November presidential election.

The Committee on Foreign Investment in the United States, which is reviewing the agreement, has warned the companies that the merger could pose risks to American national security. The interagency panel has yet to make a recommendation to the president about whether the deal should be blocked.

The Biden administration signaled this month that it was preparing to block the deal before November. Following public criticism from business groups that the review process was being politicized, officials suggested last week that a decision could be delayed until after the election.

Mr. Burritt dismissed the negative talk about the deal on Tuesday and insisted that it would benefit American workers.

He also laid out the implications for U.S. Steel if the deal were to be blocked. Mr. Burritt said the company would continue to focus its resources on “mini mills” that it operates in the South rather than the larger facilities in Pennsylvania and Indiana that Nippon has said it will upgrade.

Describing the company’s current strategy as “better, not bigger,” Mr. Burritt said, “with Nippon, it would be better and bigger.”

Mr. Burritt has warned that the company could lay off workers and relocate its headquarters outside Pennsylvania if the deal were blocked.

Critics have said that the deal could threaten national security by ceding a key part of America’s manufacturing supply chain to a foreign-owned company. Biden administration officials have also raised concerns that if Nippon controls U.S. Steel, it could raise objections to American tariffs on steel imports.

Mr. Burritt noted that Japan is America’s closest ally in Asia and argued that the deal would curb China’s steel dominance.

“Bringing Nippon’s expertise with U.S. Steel’s footprint here in the United States — that investment coming in — gives us an opportunity to really compete with China,” he said.

Nippon’s bid for U.S. Steel, which was accepted in December, continues to face strong opposition from the powerful steelworkers’ union. The union has expressed fears about the future of its pension program and raised doubts that Nippon will make the investments in U.S. Steel facilities that it has promised.

In a letter to its members on Tuesday, the leaders of the steelworkers’ union reiterated their problems with Nippon’s proposal.

“The U.S. government should reject the deal for obvious and important national defense reasons, and U.S.S. can remain an independent company,” David McCall, president of United Steelworkers, and Mike Millsap, chairman of the negotiating committee, said in the letter. “We must remain united as we fight to keep U.S. Steel an American steel company that is domestically owned and operated.”