WASHINGTON - U.S. tax authorities on Thursday said that 1.4 million taxpayers have used an $8,000 home buyer tax credit so far and reminded home buyers they need to close on a purchase before the Dec. 1 deadline to qualify.

White House economic advisers are mulling whether the credit should be extended as the Obama administration seeks to ensure that recent signs of stabilization in the housing market have staying power.

The real estate industry is lobbying for a credit extension through 2010, arguing that pulling the credit now could derail the nascent economic recovery. The industry also wants it broadened to all buyers of primary residences, not just first timers.

Sales of previously-owned homes rose in July for the fourth straight month, hitting an annual rate of 5.24 million units, the highest since August 2007, the National Association of Realtors said last month.

Separately, Senate Majority Leader Harry Reid said he is co-sponsoring a bi-partisan bill to extend the credit for six months, citing his home state of Nevada's struggling housing market.

Critics of the credit say it mostly helps those who were very likely to buy without the extra cash, and that it unfairly subsidizes owners over renters.

A spokesman for the Realtors group, Walter Molony, said the 1.4-million total came in within the trade group's expectations.

The group estimates the credit will spur about 350,000 first time purchases that would not have occurred without it this year.

The credit, which was extended as part of a stimulus package passed by Congress earlier this year, can be used if a taxpayer has not purchased a home within three years, and is subject to other criteria, including income limits. (Editing by Kenneth Barry)