NEW YORK - The government's first-time homebuyer tax credit has spurred a significant amount of sales this year and its positive impact on the hard-hit housing market warrants an extension, an economist known for her property market expertise said on Thursday.

Celia Chen, senior director of housing economics at Moody's in West Chester, Pennsylvania, said the government's $8,000 tax credit for first-time home buyers -- part of its economic stimulus bill -- has helped pave the way for stabilization.

They estimate that it will have generated 400,000 additional sales by the time the program ends at the end of November, which will amount to about 8 percent of all sales this year, she said.

With the tax credit about to expire, its positive impact is waning, however, as reflected in the weak September new home sales, she said.

The U.S. Senate's top Democrat and top Republican each voiced support on Wednesday for extending and expanding a soon-to-expire tax credit aimed at boosting the fragile housing market, though a vote on the measure could be delayed until next week.

Key senators agreed to extend the $8,000 first-time home buyer tax credit, which expires at the end of next month, through April of next year, sources familiar with the matter told Reuters.

The U.S. housing market has suffered the worst downturn since the Great Depression and its impact has rippled through the economy. While the sector has found some footing after a three-year slump, it remains highly vulnerable to setbacks.

Low mortgage rates, high affordability and the government's $8,000 tax credit for first-time home buyers have helped.

An extension of the credit would be helpful for an economy and housing market that remain fragile, she said. (Additional Reporting by Andy Sullivan, Corbett B. Daly and Lisa Lambert in Washington)