WASHINGTON — Democrats seeking a deal to avert the year-end “fiscal cliff” are trying to etch into stone the signature economic achievement of Republican President George W. Bush by permanently extending tax cuts enacted during his tenure.

President Barack Obama has put the extension of the tax cuts for most Americans at the top of his domestic agenda, a remarkable turnaround for Democrats, who had staunchly opposed the tax breaks when they were written into law about a decade ago.

The main dividing line between Republicans and Democrats now has come down to whether tax rates should increase for top earners at the end of the year, when the Bush-era tax cuts are set to expire. While Republicans want to extend all of the tax cuts, Democrats are pushing to maintain lower rates on household incomes below $250,000. Those lower rates significantly reduce the taxes of nearly all American households that earn less than $250,000 — and many who earn more, even if tax rates are allowed to increase on incomes above that figure.

While it is increasingly unlikely that the two parties will reach agreement to avoid the fiscal cliff before Jan. 1, it is all but certain that their ultimate deal, whenever it comes, will make permanent the lower rates for most Americans.

R. Glenn Hubbard, dean of Columbia Business School and an architect of the Bush tax cuts, said it was “deeply ironic” for Democrats to favor extending most of them, given what he called their “visceral” opposition a decade ago. Keeping the lower rates even for incomes under $250,000 “would enshrine the vast bulk of the Bush tax cuts,” he said.

Democrats say they have reconsidered their opposition to the Bush tax cuts for several reasons. The cuts were written into law from 2001 to 2003 after a decade in which most Americans had seen robust income growth. Over the past decade, by contrast, median wages have declined, after adjusting for inflation, amid a weak economy. Allowing tax cuts for the middle class to expire would further reduce take-home pay.

“We’ve had these tax cuts in place since 2001. The world changes, and the economy is where it is,” said Steven Elmendorf, who was chief of staff to former House minority leader Richard Gephardt, D-Mo., a primary opponent of the Bush tax cuts. “With people’s economic status, we should not be raising taxes on people earning under $250,000.”

What’s more, income inequality has been growing. Sparing the middle class higher taxes while requiring the wealthy to pay more would tip the scales slightly in the other direction.

“The reason there’s been this movement toward broad consensus on renewing the tax cut for working- and middle-class families is that will give us a sharper progressivity in the tax system that is very much desired by Democrats and progressives who’ve seen an income distribution more and more distorted toward the wealthy,” said Betsey Stevenson, former chief economist in Obama’s Labor Department and a professor at the University of Michigan, who added that taxes may have to rise even more than currently contemplated to meet the country’s needs.

More than economics

But more than economics is at work. Democrats have found what they consider a winning political argument in calling for lower taxes on the middle class and higher taxes on the wealthy. And while, a decade ago, many Democrats favored maintaining higher tax rates to help fund domestic programs, it is much harder to take away a tax cut than make it in the first place.

“Most fundamentally, it was due to a perception by Democrats that the political reality was moving to the right on economic policy,” said Jim Manley, a former top aide to Senate Majority Leader Harry Reid, D-Nev. “The Democratic Party has adjusted to those realities and recognizes you’ve got to be more careful about focusing on the middle class.”

Even as they agree that taxes shouldn’t rise on the middle class when the economy is still weak, some liberals are worried by the prevailing Democratic view that the bulk of the Bush tax cuts should be made permanent. Liberals fear that lower revenue means less money for domestic programs, such as education, as well as for the social safety net.

The Bush tax cuts involve a long list of tax provisions, including lower federal income-tax rates for all Americans, lower tax rates on investment income such as capital gains and dividends, and tax benefits for married couples with children. The scheduled expiration of the Bush tax cuts, combined with an end to other temporary tax cuts enacted more recently by Obama and deep spending cuts constitute the fiscal cliff, which is to take effect in January barring new action by Congress. These dramatic fiscal changes could tip the U.S. economy back into recession.

Although primarily targeted toward households earning less than $250,000, the middle-class component of the Bush tax cuts also benefits those earning above that. The first $250,000 earned by even the wealthiest families would be subject to low rates. For this reason, Obama noted last month that under his proposal, “every American, including the wealthiest Americans, gets a tax cut.”