In a letter the Social Security Administration sent to its employees’ union, agency officials said that while no decision about a furlough had been made, one was possible "given the potential of reduced congressional appropriations."

The letter was circulated by congressional Democrats, who said in a written statement that such cuts could mean shuttered Social Security offices and delayed benefit payments. The letter’s distribution by Democrats underscored how the threat of jeopardizing Social Security payments is a potent political weapon.

GOP lawmakers accused Democrats of "irresponsible scare tactics," and said their proposed cuts would not affect benefits or force the Social Security Administration to close offices. Any furloughs "would result only if that decision were made by the administration," House Ways and Means Committee Chairman Dave Camp, R-Mich., said in a written statement.

Republicans are pushing a huge spending bill through the House that would impose deep cuts on domestic programs.

The overall bill is the first step in an increasingly bitter struggle between Democrats and Republicans over how much to cut federal agencies’ funding over the second half of the budget year that ends Sept. 30. Current funding runs out March 4 and a temporary spending bill will be needed to avoid a government shutdown.

Republicans say the legislation would pare Social Security’s administrative budget by $125 million from current levels plus another $500 million from a reserve fund. Democrats say the cut would leave the agency with $1.7 billion less than President Barack Obama requested.

As Friday’s debate began, the focus was on Obama’s health care overhaul, which dominated Congress’ work in 2009 and was enacted last year. The GOP has virtually no chance of killing the law because of support for the program from Obama and the Democratic-run Senate, but House Republicans have been trying relentlessly to chip away at it.

"It’s a law designed by those who wish to control every health care decision made by health care providers and patients, by every employer and employee, by every family and individual," said Rep. Denny Rehberg, R-Mont., who sponsored one of several amendments blocking health overhaul money.

Rep. Rosa DeLauro, D-Conn., said the GOP effort would "put insurance companies back in charge, further demonstrating the majority’s special-interest priorities and hypocrisy on job creation and deficit reduction."

Action expected Friday also included votes on a proposal to block federal aid to Planned Parenthood, bar the Pentagon from spending taxpayer money to sponsor NASCAR race teams; to reverse a proposed Obama administration rule that seeks to crack down of for-profit colleges and vocational schools; and to strip the Environmental Protection Agency of its authority to issue regulations on global warming.

With a government shutdown possible if the spending measure isn’t extended at least temporarily, House Speaker John Boehner, R-Ohio, inflamed the situation Thursday by insisting that the GOP-controlled House would refuse to approve even a short-term measure at current spending levels.

"Read my lips: We’re going to cut spending," Boehner declared. Democrats immediately charged that Boehner was maneuvering Congress to the precipice of a government shutdown.

The GOP would reduce spending to about $60 billion below last year’s levels, mixing an increase of less than 2 percent for the Pentagon with slashing cuts averaging about 12 percent from non-Pentagon accounts. Such cuts would feel almost twice as deep since they would be spread over the final seven months of the budget year.

The Environmental Protection Agency and foreign aid accounts would be especially hard hit, while GOP leaders orchestrated just a modest cut to Congress’ own budget.

Some of the most politically difficult cuts, to grants to local police and fire departments, special education and economic development grants, were reversed. Amtrak supporters easily withstood an attempt to slash its budget.

But with the fiscal framework of the measure already saddled with a veto threat, Republicans mounted an assault on the administration’s regulatory agenda. By a 244-181 tally Thursday, Republicans voted to block the Federal Communications Commission from enforcing new rules that prohibit broadband providers from interfering with Internet traffic on their networks. The new "network neutrality" rules are opposed by large Internet providers.

Republicans then moved, on a 250-177 vote, to stop the Environmental Protection Agency from imposing limits on mercury pollution from cement factories. Supporters said the new rules would send American jobs overseas, where air quality standards are more lax or non-existent.

Republicans also turned back Democratic attempts to boost funding for the Securities and Exchange Commission and the Commodities Futures Trading Commission, whose budgets would be cut sharply under the measure, to pay for responsibilities added in last year’s overhaul of federal financial regulations.

Social issues also came into play.

Thursday night’s action was dominated by a lengthy debate on an amendment by Rep. Mike Pence, R-Ind., a strong foe of abortion, to block Planned Parenthood from receiving any federal money. The organization provides a variety of women’s health services.

"It is morally wrong to take the taxpayer dollars of millions of pro-life Americans and use them to fund organizations that provide and promote abortion, like Planned Parenthood of America," Pence said.

Democrats said Planned Parenthood provides much-needed access to contraception, medical exams and counseling to women and that federal law already prohibits the use of government funds for abortions in most circumstances.

Rep. Nita Lowey, D-N.Y., said the GOP proposal would "make it harder to access pap tests, breast exams, routine gynecological examinations, flu vaccinations, smoking cessation services, cholesterol screening, contraceptives, and all of the other services that Planned Parenthood provides."

Liberal Minnesota Democrat Betty McCollum hoped to team up with tea party-backed GOP freshmen to bar the Pentagon from spending taxpayer dollars to sponsor NASCAR race teams. She said such sponsorships can cost millions of dollars, simply for placing decals on race cars and for a few driver appearances.

The Army, the Air Force and the National Guard each sponsor cars with the aim of boosting military recruitment, but the Navy and Marine Corps dropped their NASCAR sponsorships in recent years, saying they didn’t know whether they were effective.