Debt Talks in Disarray as House Balks By JONATHAN WEISMAN WASHINGTON — With the federal government on the brink of a default, a House Republican effort to end the shutdown and extend the Treasury’s borrowing authority collapsed Tuesday night as a major credit agency warned that the United States was on the verge of a costly ratings downgrade. After the failure of the House Republican leadership to find enough support for its latest proposal to end the fiscal crisis, the Senate’s Democratic and Republican leaders immediately restarted negotiations to find a bipartisan path forward. A spokesman for Senator Harry Reid of Nevada, the majority leader, said Mr. Reid was “optimistic that an agreement is within reach” with Senator Mitch McConnell of Kentucky, the Republican leader. With so little time left, chances rose that a resolution would not be approved by Congress and sent to President Obama before Thursday, when the government is left with only its cash on hand to pay the nation’s bills. “It’s very, very serious,” warned Senator John McCain, Republican of Arizona. “Republicans have to understand we have lost this battle, as I predicted weeks ago, that we would not be able to win because we were demanding something that was not achievable.” A day that was supposed to bring Washington to the edge of resolving the fiscal showdown instead seemed to bring chaos and retrenching. And a bitter fight that had begun over stripping money from the president’s signature health care law had essentially descended in the House into one over whether lawmakers and their staff members would pay the full cost of their health insurance premiums, unlike most workers at American companies, and how to restrict the administration from using flexibility to extend the debt limit beyond a fixed deadline. Even so, the House speaker, John A. Boehner, Republican of Ohio, and his leadership team failed in repeated, daylong attempts to bring their troops behind any bill that would reopen the government and extend the Treasury’s debt limit on terms significantly reduced from their original push against funding for the health care law. The House’s hard-core conservatives and some more pragmatic Republicans were nearing open revolt, and the leadership was forced twice to back away from proposals it had floated, the second time sending lawmakers home for the night to await a decision on how to proceed Wednesday. “We’re trying to find a way through it,” said Representative Greg Walden of Oregon, the chairman of the National Republican Congressional Committee, emerging from Mr. Boehner’s office to announce that no votes would be held Tuesday night. The House setback returned the focus to the Senate, where the leadership had suspended talks after the Senate Republican leadership opted to give the House a chance to produce an alternative to the Senate measure taking shape. Under the emerging Senate deal, the government would be funded through Jan. 15 and the debt limit extended until Feb. 7. House and Senate negotiators would be required to reach accord on a detailed tax-and-spending blueprint for the next decade by Dec. 13. A proposal to delay the imposition of a tax on medical devices had been dropped from the deal, as had a complicated tax on self-insured unions and businesses participating in the health care exchanges. All that remained for Republicans was language tightening income verification for people seeking subsidies on the insurance exchanges, but that language was still being negotiated. It remained unclear if the Senate plan could pass the House or even if Mr. Boehner would bring it forward for a vote. The hopes for a resolution by Thursday also appeared to rest with the senators who had begun the failed movement to tie any further government funding to the gutting of the Affordable Care Act: Ted Cruz, Republican of Texas, and Mike Lee, Republican of Utah. If Mr. Reid and Mr. McConnell reach a final accord, Senate leaders expect to use a parliamentary maneuver that will allow the majority leader to quickly move the deal to the Senate floor on Wednesday. With unanimous consent, a final vote would come the same day. But if Senate hard-liners object, the Senate would have to wait until Friday, then muster 60 votes to cut off debate. Further obstruction would mean the final vote would happen Saturday, when the bill would go back to the House, where it would pass only if it had overwhelming Democratic support since many Republicans would not vote for it.