More than 1.4 million Americans have claimed an $8,000 tax credit for first-time home buyers since the program took effect on Jan. 1, according to a recent report by the Internal Revenue Service.

But housing industry advocates are concerned that a recent spike in home sales attributed to the credit may be undone when the incentive expires on Dec. 1, CNNMoney.com reported.

“Just like the Cash for Clunkers program, there could be a hangover effect,” said Mike Larson, a real estate analyst for Florida-based Weiss Research Inc.

The growing concern has led the National Association of Realtors (NAR), which estimates that the incentive will result in an additional 350,000 sales, to call for an extension of the program.

“We do think that housing will recover without it, but the market will come back faster and stronger with it,” NAR spokesman Walter Molony said. “We’re calling for extending the credit until the end of next year and expanding it to all homebuyers.”

There are six bills before Congress that would prolong the credit, including four in the House of Representatives that would extend the Nov. 30 deadline through at least the end of December 2009, and two in the Senate that would extend it through 2010.

“If we don’t extend and expand the program, the seeds of growth planted could (die),” said Jerry Howard, president of the National Association of Home Builders.

An analyst with Concept Capital’s Washington Research Group said the extension has a 60 percent chance of being passed.

More than $14 billion already has been allocated to the program, which is available to anyone who is purchasing a primary residence, hasn’t owned a home for three consecutive years prior to purchase and earns less than $75,000 for individuals and less than $150,000 for couples.