WASHINGTON — Budget cuts have forced the Social Security Administration to close dozens of field offices even as millions of baby boomers approach retirement, swamping the agency with applications for benefits, a senior agency official told Congress Wednesday.

Better Internet access and more online services are easing the transition, said Nancy Berryhill, the agency’s deputy commissioner for operations.

“We are fully committed — now and in the future — to sustaining a field office structure that provides face-to-face service for those customers who need or prefer such service,” Berryhill told the Senate Special Committee on Aging. “We also understand, however, that customer expectations are evolving due to changes in technology, demographics and other factors.”

Senators appeared unconvinced. “The fact of the matter is, millions of seniors and disabled Americans are not accustomed to doing business online,” said Sen. Susan Collins of Maine, the top Republican on the Aging Committee. “Even as computer and broadband technologies become more widespread, the idea that the Social Security Administration can serve beneficiaries primarily online ignores the very real needs of the senior and disabled populations.”

The committee held a hearing Wednesday after issuing a bipartisan report showing that Social Security has closed 64 field offices since 2010, the largest number of closures in a five-year period in the agency’s history.

In addition, the agency has closed 533 temporary mobile offices that often serve remote areas. Hours have been reduced in the 1,245 field offices that are still open, the report said.

As a result, seniors seeking information and help from the agency are facing increasingly long waits, in person and on the phone, the report said.

“They don’t do any kind of analysis on what would happen to a community when their field office closes, including figuring out how the most vulnerable populations would make their way to the next-closest office,” said Sen. Bill Nelson, D-Fla., chairman of the Aging Committee.

The closings come as applications for retirement and disability benefits are soaring, a trend that will continue as aging baby boomers approach retirement.

More than 47 million people receive Social Security retirement benefits, nearly a 20 percent increase from a decade ago. About 11 million people receive Social Security disability benefits, a 38 percent increase from a decade ago.

The Social Security Administration has been encouraging people to access services online. The agency has upgraded its website in recent years, including secure connections to access confidential information. People can apply for benefits without ever visiting Social Security offices.

In 2013, nearly half of all retirement applications were filed online, the report said.

But the committee report notes that many older Americans lack access to the Internet or might not be comfortable using it to apply for benefits.

Last year, more than 43 million people visited Social Security field offices. About 43 percent of those seeking an appointment had to wait more than three weeks, up from just 10 percent the year before, the report said.

About 10 percent of visitors to Social Security offices are applying for benefits, Berryhill said. The largest group, about 30 percent, are seeking new or replacement Social Security cards.

Berryhill said Social Security officials do annual reviews to determine whether offices should be expanded, reduced or closed.

“Once we make the decision to consolidate an office, we discuss the changes with stakeholders,” Berryhill said. “We hold town hall meetings or other forums that allow the public to voice their concerns. We contact key community leaders.”

Like many federal agencies, Social Security has faced budget cuts in recent years. After two years of shrinking budgets, the agency got a 6 percent increase this year, to $11.8 billion.

Social Security has cut its workforce by 11,000 employees over the past three years, Berryhill said.

She said the agency saves an average of $4 million over the course of a decade for every field office it closes.

“I can hire a lot of employees with $4 million,” Berryhill said.