Prime Minister Keir Starmer of Britain reversed course on proposed changes to a key social welfare benefit on Friday after pressure from critics, the latest in a series of political retreats that have shaken his leadership.

Confronted by a rebellion from its own lawmakers, the government announced that it would weaken proposals to change the eligibility requirements for payments to disabled people, a move that was expected to affect hundreds of thousands of people.

The proposed legislation is designed to reduce the country’s ballooning welfare bill. The government is hoping that its concession will be sufficient to win a vote in Parliament, scheduled for Tuesday, that it had looked almost certain to lose.

Mr. Starmer’s reversal follows a similar retreat over a plan to restrict payments to help retirees with winter fuel costs, and a change of heart when he opted to hold a national investigation into child sexual exploitation and abuse — an inquiry that he had previously rejected.

The welfare changes were proposed in the hope of reducing government spending by 5 billion pounds, about $6.9 million. But Friday’s turnabout leaves the government, despite its large parliamentary majority, in a political crisis less than a year after achieving a decisive general election victory.

Opposition critics have predicted that to make up the shortfall, Rachel Reeves, the chancellor of the Exchequer, will have to raise taxes, cut government spending elsewhere or break her self-imposed rules on borrowing.