The “Buffett Rule’’ — the Democratic-authored effort to impose a minimum tax on millionaires — is probably dead for awhile, fatally wounded by a largely partisan Senate vote Monday.

The 51-45 procedural vote failed by nine votes, since 60 are needed to cut off debate.

But both sides scored political points. Democrats painted the higher tax as a fairness issue. Republicans countered that higher taxes would stymie the already sluggish economy.

Monday’s drama, the day before the filing deadline for federal income tax returns, was the opening round of what promises to be a week of congressional maneuvering for advantage on the tax issue. The House of Representatives is expected to vote later this week on a Republican-backed plan to give small businesses a tax break.

No proposal, though, has been as incendiary as the “rule” named for Warren Buffett, the billionaire investor who last year said his secretary pays taxes at a higher rate than he does.

With a strong push from President Barack Obama, Democrats want to end that disparity by generally imposing at least a 30 percent tax on millionaires _ more than twice the rate that presumptive Republican presidential nominee Mitt Romney, a multimillionaire, paid in 2010.

“It’s an important message for Washington to be able to send to middle-class taxpayers as they sit down to pay their taxes,” said Sen. Sheldon Whitehouse, D-R.I., the Senate bill’s chief author.

Liberal groups were adamant that the Senate vote was an important political demarcation line.

“The Buffett Rule, if enacted, would mean that Wall Street CEOs and big oil executives would not pay lower taxes than their secretaries and chauffeurs. This is a no-brainer. The senators who oppose this minimal standard have shed all sense of decency,” said Robert Borosage, co-director of the liberal Campaign for America’s Future. “Only the corrupt or the morally bankrupt could vote to protect the ability of the richest Americans to pay a lower rate of taxes than the rest of us.”

Republicans, though, insisted that the tax was little more than a ploy that few voters cared about. Romney has proposed a 20 percent across-the-board cut in all marginal income tax rates, and congressional Republicans are exploring ways to overhaul the entire tax code.

“The bill is a political gimmick that’s supposed to distract Americans from the president’s miserable record instead of solving problems,” said Sen. John Barrasso, R-Wyo., chairman of the Senate Republican Policy Committee.

No such sweeping steps are likely to pass Congress before the November elections. Instead, Congress is likely to take a series of votes aimed at illustrating each party’s position in hopes that the voters will give them a mandate for their approach.

Later this week, the Republican-dominated House of Representatives is likely to vote on a GOP plan to provide a 20 percent tax deduction to certain small businesses.

Democrats vow they won’t give up on trying to impose higher taxes on the wealthy. “We’ll keep pushing this issue all year long,” insisted Sen. Charles Schumer of New York, the Senate’s third-ranking Democrat.

Democrats are trying to paint Romney, the son of an auto executive and former Michigan governor, as a rich, out-of-touch patrician with little sensitivity to the plight of middle- and lower-income wage earners.

The nonpartisan Tax Foundation estimates that most Americans pay an effective tax rate, on average, of 11 percent.

Romney is worth $190 million to $250 million. Most of his taxable income comes from investments rather than wages, taxed at the rate of capital gains, which for the most part is 15 percent. His tax records for 2010 show that he and his wife, Ann, had an effective tax rate of 13.9 percent of their income after deductions. Romney has asked for an extension in filing his 2011 return.

Obama’s family income is largely from wages and book-sale profits. Last year, the first family paid tax at a 20.5 percent rate.