Once again, we’re at the brink.

With much of the government due to run out of money on Friday, Senate Majority Leader Harry Reid, D-Nev., is gambling he can force congressional Republicans to blink on year-end payroll-tax and appropriations bills.

It’s no secret that Reid has threatened for weeks to keep the Senate in session until deals with House Republicans allow passage of both packages. But now he has upped the ante by refusing to allow passage of an omnibus appropriations bill until Republicans agree to extend the payroll-tax holiday for one year, continue federal unemployment insurance, and prevent a scheduled reduction in Medicare pay to doctors.

By simply withholding Democratic signatures from the conference report for fiscal year 2012’s remaining nine spending bills—and thus blocking movement of the appropriations package—Reid is using what may be his last point of leverage to get Republicans to negotiate seriously toward a compromise on the other year-end measures. On Tuesday night, he called the House-passed version of a payroll-tax-cut package “dead on arrival.”

Reid’s strategy—endorsed by the White House—will almost certainly force enactment by Friday of another short-term spending bill to prevent a government shutdown. That’s when the current temporary funding measure expires.

By late Tuesday night, Republicans were conceding that another continuing resolution like the ones that have kept most of the government funded since Oct. 1 would likely be necessary.

Whether Reid’s gambit is a bona fide pressure mechanism to get House Speaker John Boehnerof Ohio and other Republicans to relent on policy riders like the Keystone XL pipeline or offsets to pay for the payroll-tax cut is less certain. Reid certainly has the muscle to block consideration, and Democrats in the House have rare leverage, too. House Minority Whip Steny Hoyer, D-Md., will deny the GOP omnibus votes until a deal on the payroll tax-cut package is reached, Democratic aides said. With just 53 votes, Senate Democrats always need GOP votes to get the 60 required for most action in the chamber.

Congressional leaders want to pass both packages by next week. But both sides took a hard line on Tuesday as House Republicans pushed their preferred payroll-tax cut and unemployment extension bill through that chamber in a 234-193 vote.

Though Democrats insist that a deal on the outstanding appropriations bills will be reached, Reid’s brinksmanship may increase chances of at least a brief government shutdown. Republicans, meanwhile, hope that by standing pat, they will force Reid to back down and largely accept the House’s payroll tax bill and omnibus.

“We think they’ll blink,” said one Senate GOP leadership aide.

Some Democrats and Republicans say appropriators have a deal on the giant spending bill, despite talk by Reid and the White House of lingering issues.

Those issues relate mostly to Republican policy riders ranging from such items as tightening rules for travel and money transfers to Cuba, to restrictions on funding abortions in Washington, D.C., to changes in the budget of the Commodity Futures Trading Commission. The attachment of some of these riders is contentious, acknowledge some Republicans, but agreement on their inclusion was reached nonetheless, they say.

Top House GOP aides warn that Reid is playing a game of chicken he may come to regret.

“He clearly just wants to run out the clock until Christmas, where he thinks we’ll cut a desperate deal,” said a member of the House GOP leadership’s inner circle. “He hasn’t learned much about our members this year. They would be just fine with passing our bill today and then another CR and telling Reid to call when the Senate passes something.”

Reid said Democrats have not reneged on any appropriations deal and that agreement is “very close.” As for the House GOP’s payroll tax-cut package, he said: “They’re wasting time catering to the tea party folks over there when they should be working with us on a bipartisan package that can pass both houses.”

Reid will force a vote this week in which Democrats will reject the House-passed bill, Senate Democratic aides said. Democrats are working on an alternative measure, but it is not clear when they will offer it.

Like the GOP plan, the Democratic alternative would extend the payroll-tax cut and unemployment benefits and address the Medicare doctors’ pay issue, Democratic aides said. However, it would also extend popular tax breaks such as the research-and-development tax credit, education credits, and small-business credits that typically win Republican support, something not included in the House-passed bill.

House Ways and Means Committee Republicans said the GOP would let most of those provisions temporarily expire with the expectation that an extension would be passed in January.

Those additions would have an expensive, $35 billion price tag.

Reid said Democrats would retain a surtax on incomes of more than $1 million a year as a way to pay for some of the package. Inclusion of that provision probably ensures Republicans will defeat the Democrats’ alternative. With both the House plan and Senate Democrats’ package defeated, Reid will have a minor obstacle to overcome. The Constitution requires all spending measures to originate in the House. However, Senate Democratic aides say that problem can be quickly solved if a deal is brokered.

Meanwhile, the White House is working to solidify backing behind Reid’s strategy.

President Obama will do “what he needs to do” to keep Congress in town until it gives him the extension of the payroll-tax cut he has demanded, the White House said in a statement on Tuesday night. But senior officials wouldn’t go so far as to admit that the president struck a deal with Reid to hold the omnibus package hostage until he gets what he wants.

The president is “making clear that he is not going to accept Congress leaving Washington and the middle class holding the bag here by seeing its taxes go up,” said White House press secretary Jay Carney. “So he will do what he needs to do, working with like-minded members of Congress, to ensure that Congress extends the payroll-tax cut, extends unemployment insurance, and gets the rest of its work done.”