WASHINGTON — Short of support from their conservative members, House Republican leaders on Thursday abruptly put off a vote on their proposal to raise the debt ceiling and cut government spending, throwing last-ditch efforts to avert a government default next week into disarray.

Just minutes from a roll call vote on the plan pushed by Speaker John A. Boehner, Republicans stunned the House by interrupting the debate and turning to routine matters while Mr. Boehner and his lieutenants tried to pressure reluctant conservatives into backing their plan. The House then went into a recess and shortly before 11 p.m., the leadership announced that no vote would be held Thursday.

It was unclear if the leadership intended to reconfigure the measure and try again Friday, but senior lawmakers were taking procedural steps to do so.

The surprise postponement threw the endgame of the debt-limit clash into confusion and raised concerns among some on Capitol Hill that the government was lurching toward a default. The White House and Senate Democratic leaders had been waiting for the House to act before making their next move with an eye on the Tuesday deadline set by the Treasury Department for raising the debt ceiling or facing the possibility that the government would not be able to meet all its financial obligations.