WASHINGTON — Next to the oath of office, it has been perhaps the most important commitment that Republicans in Congress can make. It is called simply "the Pledge," and its enforcer is such a fixture in the party that he is known simply by his first name, Grover.
Signing it means a promise never, ever to vote for a tax increase.
But the pledge and its creator, Grover Norquist, a 56-year-old conservative lobbyist, have never before faced a test as they do now. The federal deficit stands at $1 trillion. The social safety net continues to grow — and, in the case of Medicare and Social Security, remains hugely popular. And unless the two parties can agree on a fiscal plan before Jan. 1, hundreds of billions of dollars of tax increases will go into effect automatically, meaning that Congress does not even need to act for taxes to rise.
The combination means that Mr. Norquist, whose long record of success is a rarity in Washington, finds himself in a tricky spot. Some top Republicans, including Speaker John A. Boehner, are saying they now agree with Democrats that the government must collect more tax revenue. Others have gone so far as to break with Mr. Norquist publicly.
By Mr. Norquist's count, 219 House members — enough for a majority — and 39 senators have committed to the pledge. But some of those members who signed on, many of them years ago, have started to back away, apparently leaving him several votes shy of the majority he would need to block any tax increase.
"A pledge is good at the time you sign it," said Representative Peter T. King, a New York Republican whose name still appears as a pledge signer on the Web site of Mr. Norquist's group, Americans for Tax Reform. "In 1941, I would have voted to declare war on Japan. But each Congress is a new Congress. And I don't think you can have a rule that you're never going to raise taxes or that you're never going to lower taxes. I don't want to rule anything out."
Mr. Norquist contends that every few years, several noisy Republicans say their support is squishy. Yet every time, he says proudly, the outcome is the same.
"It's been 22 years since a Republican voted for a tax increase in this town," he said in a recent interview. "This is not my first rodeo."
Ask Republicans in Congress today what they think of the pledge, and many of them say that while they still subscribe to a low-tax view of government, they resent being hamstrung by a piece of paper they signed well before they were elected. Some of them are even saying they want out.
"I'm frankly not concerned about the Norquist pledge," Senator Saxby Chambliss of Georgia said last week.
Senator John McCain noted with a certain sense of satisfaction at an Atlantic magazine forum last week that "fewer and fewer people are signing this, quote, pledge."
Senator Lindsey Graham of South Carolina, at the same forum, said that with the federal debt at $16 trillion, closing tax loopholes and eliminating deductions have to be considered, "even though that may technically violate the pledge." He added, "Sign me up."
Senator Tom Coburn of Oklahoma has called the pledge a "tortured vision of tax purity."
Ted Yoho, who will represent part of northern Florida when the new House convenes in January, said: "I'll pledge allegiance to the flag. I'll pledge to be faithful to my wife." But he is one of a handful of House newcomers who declined to sign to Mr. Norquist's pledge and likened it to a New Year's resolution that many others will break.
Mr. Norquist claims to have invented the idea for a no-new-taxes promise when he was a 12-year-old volunteer for Richard M. Nixon's 1968 presidential campaign.
He is fond of evocative metaphors, like claiming he wants to reduce government "down to the size where we can drown it in the bathtub." Not honoring the pledge would cause grave damage to the Republican brand, he has said, likening it to a Coke can with a rat head in the bottom.
The walls at the headquarters of his interest group are covered with signed copies from conservative heroes like Newt Gingrich, who warns Republicans to stick to their guns. Mr. Gingrich, like Mr. Norquist, argues that the pledge protects Republicans from agreeing to stealth tax increases that ultimately hurt them.
"Every time I've watched Republicans try to be clever with Democrats on issues of taxation," Mr. Gingrich said last week, "Democrats have won."
In the current talks with President Obama, Republicans have signaled an openness to increasing tax revenue by reducing deductions and credits, as long as income tax rates do not rise. That would still violate the pledge, which states that "any and all efforts" to increase taxes are inexcusable.
Some Republicans have decided that they no longer like the lack of flexibility. "Basically the pledge is like a Master lock," said Representative Scott Rigell of Virginia, who in January became one of the first freshmen to publicly renounce the pledge.
When Mr. Rigell announced his reversal, he braced for the consequences. Instead, he said, the word he received was a text message from his local Republican Party chairman saying, "Thanks for your courage." Yet Mr. Norquist still includes Mr. Rigell's name on his list of pledge signers.
Obama administration officials and other Democrats argue that Mr. Norquist's pledge is doomed because Republicans will eventually need to square their budget policies with public opinion. With society aging and modern medicine developing new treatments, health care costs will continue to rise.
Voters express strong support for Medicare and Social Security and for raising taxes on the affluent, Democrats note. Over all, federal tax revenue has taken up a smaller share of gross domestic product in the last few years than at any point since the 1950s. One possibility is that the pledge will survive on a technicality. If Congress fails to reach a resolution before the tax cuts passed during the George W. Bush administration expire at midnight on Dec. 31, rates will revert to their higher pre-2001 levels. If Congress then approved a bill that restored only some of those lower rates but not, for example, ones for the highest income brackets, Republicans could still claim to be within the bounds of their pledge.
But Mr. Norquist argues that history suggests the pledge will survive on more than a technicality. Republicans, he said, have always come around, even if it takes a little pressure.
When he hears about someone wavering on the pledge, he has a simple routine, he says. "Every time this happens, I call the guy and say: 'I just want to make sure we're on the same page. I don't want to have an argument,' " he said. "But if you really want to raise taxes, I do want to have an argument."