WASHINGTON &#8212 Silena Davis had counted on an early tax refund to pay for getting her teeth fixed. Now, because Congress has dawdled all year on a tax bill, she and millions of other early filers could have to wait extra weeks for refunds that averaged $2,291 last year.

The Internal Revenue Service is looking hard at delaying the start of its filing season, set to kick off on Jan. 14, if Congress fails to pass legislation in the next two weeks. At issue is how to handle what could be a dramatic increase in the number of people facing a higher alternative minimum tax.

If there is a delay and it extends into mid-February, it would slow nearly 38 million refunds worth a total of about $87 billion, the IRS Oversight Board predicts.

“It would definitely make a big difference with me,” said Davis, a George Washington University Law School administrator. “I’m going to have to get a crown, and it’s going to be really expensive.”

The board, an independent advisory group, said in a report to lawmakers last week that it is “gravely concerned about the serious risks” to the filing season if Congress does not make timely changes to the tax. They include more mistakes by both taxpayers and the IRS and more people failing to pay taxes because of uncertainty about what they owe.

The alternative minimum tax was passed in 1969 and was aimed at about 155 very wealthy families who used deductions to avoid paying any federal income tax. The AMT disallows certain deductions and credits. It was not adjusted for inflation; as a result, over the years it has hit a growing number of middle-income taxpayers.

More than 4 million were subject to it in the 2006 tax year, and that could soar to 25 million this year without congressional action.

Congress in recent years has approved one-year fixes to stop the tax from expanding. Legislation this year has stalled in a dispute between majority Democrats and the White House. The stumbling block is whether some taxes should rise to offset the cost of correcting the AMT.

Richard Spires, the deputy IRS commissioner for operations support, said in an interview that the agency is considering not processing all early returns if the AMT issue is not resolved soon.

“We are worried that if we allow certain filers to file that it does not cause a lot of confusion and delay the whole filing system for everyone,” he said.

While most people are not hit by the tax, the IRS lacks a way to distinguish what returns are affected by possible changes in tax law.

The AMT, he said, involves “some of the most complex code that we deal with, right at the heart of our tax compilations.”

People who file returns under the current AMT law would have to file an amended return if the law were changed. Spires also stressed that there would not be any advantage to filing by paper if the IRS is not accepting electronic returns. “We’re not going to process paper returns any faster,” he said.

The dispute would give the millions of people who wait until the last minute to file their returns yet one more reason to procrastinate. “If it was only two or three weeks, it wouldn’t bother me at all,” said Toni Mistretta, a health care worker from Jamesport, N.Y.

Some disruption already is taking place. As Congress was leaving for its Thanksgiving break with no deal in sight, the IRS was going to press with the forms for the 2007 tax year.

Spires said the agency has postponed printing the AMT form and 11 others affecting smaller tax issues that Congress has promised to deal with but has not.

The IRS has done the design work on the new forms after receiving assurances from Democratic and Republican leaders on the taxwriting committees that Congress will enact an AMT fix this year similar to legislation passed last year.

Congress returns this week. But it will take about seven weeks after a bill is passed and signed into law to do the necessary programming and testing before those forms could be presented to the public, Spires said.

H&R Block said 60 percent of its clients who claim credits using forms affected by pending legislation normally file by the end of February. A delayed refund could cause hardship for those people in paying holiday bills or addressing other immediate financial problems, according to the company.

Aides on the taxwriting committees said they were unaware, at this point, of any suggestions to extend the April 15 filing deadline if the filing season is contracted because of the AMT dilemma.

The IRS oversight board, using past agency data, said that if the start of the filing season is pushed back two weeks to Jan. 28, it would delay some 6.7 million refunds totaling $17 billion. A Feb. 18 starting date would delay 37.7 million refunds totaling $87 billion.

The report came after weeks of warnings – from President Bush, Treasury Secretary Henry Paulson and the IRS – about the consequences of failing to enact a temporary fix. Paulson said the 25 million returns that could be affected in 2007 would pay, on average, an additional $2,000 in federal income tax.

“This is a huge tax increase that taxpayers do not deserve and Congress must stop,” Bush said Saturday in his radio address, his latest comments on the issue.

That will not be easy.

Congress’ Joint Committee on Taxation estimates that, without a fix, about half of taxpayers with adjusted gross incomes in the $75,000 to $100,000 range will be affected by the AMT this year.