Frank Bisignano, the Wall Street veteran being considered to lead the Social Security Administration, will go before the Senate on Tuesday morning, where lawmakers will demand answers about his plans for an agency recently thrown into tumult.

The plans being laid by the Trump administration for the typically staid agency — long viewed as a third rail of government — have prompted widespread outcry given its crucial work: It delivers billions of dollars in retirement, survivor and disability payments to 73 million people each month. The agency typically evolves slowly, aware that missteps could potentially cut off cash to people who rely on it.

But in the month or so since a team from Elon Musk’s Department of Government Efficiency arrived at the agency, it has taken a series of rapid fire actions, including significant job cuts and policy changes that have rattled many advocates and employees, who fear the changes could make it difficult for vulnerable people to access benefits.

Some concerned Democratic lawmakers recently sent a letter to Mr. Bisignano asking him to promise not to privatize any of the agency’s components.

“We are gravely concerned about the current trajectory of the S.S.A. and more specifically, that those charged with leading it might profit off its destruction,” Senators Elizabeth Warren of Massachusetts and Ron Wyden of Oregon wrote.

Mr. Bisignano, who described himself in an interview on CNBC as “fundamentally a DOGE person,” has spent much of his career as a fixer for major financial institutions hoping to improve their back-end processes. He said he planned to bring the same approach to Social Security.

“The objective is not to touch benefits,” he said in the interview. “The objective is to figure out, there could be fraud, waste and abuse in there. And we build A.I. to find fraud, waste and abuse for a living. It’s going to be a tech story.”