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It's crunch time for the Buffett Rule, and President Obama used his weekly address to make an 11th-hour pitch.

Ahead of a planned Senate vote this week on a tax hike on millionaires, Obama ratchets up pressure on Congressional Republicans in an attempt to win a p.r. victory on "fairness" even if the vote fails, as is expected.

"It's pretty sensible," Obama says of the Buffett Rule, which would impose an effective minimum tax on millionaires of 30 percent.  "Most Americans support this idea. One survey found that two-thirds of millionaires do, too.  So do nearly half of all Republicans.

"We just need some Republican politicians to get on board with where the country is," he said.

A new Gallup poll found 60 percent of Americans support a law that would raise taxes on households earning $1 million a year or more.  Strong majorities of Democrats (74 percent) and Independents (63 percent) also back the proposal, while 54 percent of Republicans stand opposed.

"As many Americans rush to file their taxes this weekend, it's worth pointing out that we've got a tax system that doesn't always uphold the principle of everyone doing their part," Obama says. "This is not just about fairness.  This is also about growth.  It's about being able to make the investments we need to strengthen our economy and create jobs."

Republicans deny Obama's claims, calling the campaign for the Buffett Rule a distraction from real solutions to accelerating the economic recovery.

"This is not a serious attempt at deficit reduction, and it certainly won't fulfill his 2009 promise to cut the deficit in half," said Republican National Committee spokesman Sean Spicer. "No, the Buffett Tax is merely a political ploy."

The rule is estimated to raise an estimated $47 billion over 10 years.  The projected budget deficit in 2012 alone is more than $1 trillion.

"There's a term for political tactics like this: class warfare," Spicer said. "That's not what America voted for in 2008."

But Democrats say the tax measure is about fairness and math.

"In a perfect world, of course, none of us would have to pay any taxes," Obama says.

"But we live in the real world, with real choices and real consequences. Right now, we've got significant deficits to close.  We've got serious investments to make to keep our economy growing.  And we can't afford to keep spending more money on tax cuts for the wealthiest Americans who don't need them and didn't even ask for them," he said.

On his 2011 tax returns released Friday, Obama reported $789,000 in income and $162,000 in taxes - or an effective rate of 20.5 percent.

The Buffett Rule would not immediately raise Obama's personal tax rate - which is lower than his secretary's - because he doesn't make more than $1 million a year.  But it would more than double the rate paid by his Republican rival, Mitt Romney, who paid 13.9 percent in 2010.