No one expects the bill, which would extend low tax rates except on income of $1 million and above, to pass the Democratic-controlled Senate. President Barack Obama's latest position puts the threshold for income tax hikes at $400,000.

While the move, called "Plan B" by Republicans, may not prompt Obama to give further ground in his negotiations with House Speaker John Boehner, it could allow Republicans to argue they did what they could to stop tax hikes and the full impact of the "fiscal cliff," which the Congressional Budget Office and economists have said could trigger another recession.

"Why not put on the floor something that's what most Americans think the president is talking about, which is protecting from tax increases everybody but truly millionaires and billionaires?," said Republican Representative Pat Tiberi of Ohio.

When it dies in the Senate, he said, "that's not our problem. We can't be held responsible for what the Senate does."

Polls have consistently suggested that the public is likely to blame Republicans for failure to reach a deal ahead of the December 31 deadline for action.

After important concessions in recent days from both Obama and Boehner, Republicans expressed frustration that the president had not moved further.

The White House seemed unconcerned by the Republican tactic, and stressed Obama's willingness to compromise further.

"The president has demonstrated an obvious willingness to compromise and move more than halfway toward the Republicans," White House spokesman Jay Carney told reporters, adding that Obama is making a "good faith" effort to reach a compromise.

Still, the mood on Capitol Hill was guardedly optimistic.

Global stocks advanced to their highest levels since September. Investors shifted funds to stocks and the euro and pulled away from safe-harbor assets such as bonds, gold and the U.S. dollar.

"They've still got a long way to go, but you can't help but say that the odds are better today than they were on Friday that we'll get some sort of agreement," said Oklahoma Republican Representative Tom Cole.

Hopes of an accord rose Monday night after Obama made a concession with his offer to limit tax increases to incomes exceeding $400,000 per household. That is a higher threshold than the $250,000 that the president had sought earlier.

Boehner, the top Republican in Congress, had earlier conceded on Obama's insistence that tax rates rise on the wealthiest Americans, but the two have been unable to agree on what income levels should be included in that category.

Analysts said Obama and Boehner may strike a compromise at $500,000 or close to that, though time was running short.

One House Republican aide, asked about prospects for "Plan B" on the House floor, said: "It wouldn't be surprising ... if a lot of conservatives balk at something like that." The House's second ranking Republican, Eric Cantor, said he was confident his party members in the House would back the bill.

'WE CAN DO BETTER'

Even as he presented the measure, Boehner said he would continue to negotiate with Obama on a broader agreement.

"Plan B is Plan B for a reason. It's a less-than-ideal outcome. I've always believed we can do better," Boehner said.

The expiration of low tax rates enacted under former President George W. Bush is a key component of the "fiscal cliff" that lawmakers are trying to prevent from taking hold next month, along with deep automatic government spending cuts.

Often challenged by the conservative wing of his caucus, Boehner held Republican lawmakers together in support of his efforts to forge a deal with Obama. The speaker emerged largely unscathed from a potentially tough meeting with his fellow House Republicans on Tuesday morning.

Representative Darrell Issa, a key committee chairman, said his fellow House Republicans "were supportive of the speaker. ... I saw no one there get up and say, 'I can't support the speaker.'"

With opinion polls showing broad support in the United States for raising taxes on the wealthiest Americans and Obama still buoyed by his re-election last month, the Republicans' traditional opposition to tax hikes has waned somewhat.

The Obama-Boehner talks have largely overcome stark ideological differences and are focused increasingly on narrower disagreements over numbers.

COST-OF-LIVING INCREASES

Obama also may face unrest from within his party. Liberal Democrats were likely to oppose a key compromise he has offered to permit shrinking cost-of-living increases for all but the most vulnerable beneficiaries of the Social Security retirement program. His proposal calls for using a different formula, known as "chained Consumer Price Index," to determine the regular cost-of-living increases, essentially reducing benefits.

"I am committed to standing against any benefit cuts to programs Americans rely on, and tying Social Security benefits to chained CPI is a benefit cut," Democratic Representative Keith Ellison said in a statement.

Obama also moved closer to Boehner on the proportion of a 10-year deficit reduction package that should come from increased revenue, as opposed to cuts in government spending. Obama is now willing to accept a revenue figure of $1.2 trillion, down from his previous $1.4 trillion proposal.

Boehner's latest proposal calls for $1 trillion in new tax revenue from higher tax rates and the curbing of some tax deductions taken by high-income Americans.

Missing from Obama's latest offer was any extension of the so-called "payroll tax holiday" that ends on January 1, bringing an immediate tax increase on wage earners.

Possible plans to produce cuts in spending for Medicare and Medicaid, the government health insurance programs for seniors and low-income Americans respectively, remained to be discussed.

Boehner and Obama have made headway on the politically explosive question of the president's ability to avoid constant battles over raising the nation's debt ceiling, which controls the level of borrowing by the government. Boehner is ready to give Obama a year of relative immunity from conservative strife over the debt ceiling, while Obama is pushing for two years.

(Additional reporting by Thomas Ferraro, Rachelle Younglai, David Lawder, Richard Cowan, Matt Spetalnick, Roberta Rampton, Jeff Mason and Fred Barbash; Writing by Kevin Drawbaugh; Editing by Alistair Bell, Will Dunham and Paul Simao)

• A Permanent Economic Emergency