(Reuters) - The U.S. Social Security Administration abandoned plans to end phone services for retirees that would have started on Monday, following a growing outcry from advocates who warned that the changes could cause chaos and further strain the agency.

The agency, which pays out $1.4 trillion in benefits to 73 million Americans annually, said on Wednesday it would "allow all claim types to be completed over the telephone," from April 14, the date that the phone option was due to be cut.

"Telephone remains a viable option to the public," the SSA said in an emailed statement to Reuters.

It gave no reason for the abrupt reversal. Just two weeks ago, the SSA said that starting Monday all retirees, widows and children would have to visit a field office if they were unable to verify their identity and apply for benefits online.

The SSA had estimated that canceling the phone option would prompt 75,000 to 85,000 more people per week to seek the help of a person at field offices, leading to roughly 4 million additional office visits annually.

Research released on Tuesday by the Center on Budget and Policy Priorities, a left-leaning think tank, found that 6 million seniors live more than 46.6 miles, round trip, from a Social Security field office, highlighting the potential burden on a demographic that may struggle to file claims online.

While individuals applying for disability or Medicare benefits were exempted from that rule, advocates and Democratic lawmakers warned that requiring potentially millions of retirees to visit an office could swamp the agency at a time when it is losing staff and its computer systems are plagued with outages.

Richard Fiesta, executive director of the Alliance for Retired Americans, said the reversal was the result of its members calling their elected officials and joining protests against the changes, pursued along with other reforms of the agency by Elon Musk's Department of Government Efficiency.

"From the moment DOGE announced its dangerous plan to eliminate SSA telephone services, our members sprang into action," Fiesta said in a statement, adding that ending phone service would have "placed an unreasonable burden on vulnerable people" and overwhelmed understaffed field offices.

The SSA, which had cited concerns about fraud when it initially announced the plan to curtail phone services, said on Wednesday it would conduct a fraud check on all benefit claims made over the telephone and flag those deemed risky.

"Individuals that are flagged would be required to perform in-person ID proofing for the claim to be further processed," the SSA said. "Individuals who are not flagged will be able to complete their claim without any in-person requirements."