NEW YORK — The nation's daily newspapers, already finding advertising revenue fall sharply because of the weak economy, saw circulation decline more steeply than last year in the latest reporting period, an auditing agency said today.

Average weekday circulation was 38,165,848 in the six-months ending in September, a 4.6 percent decline from 40,022,356 in the same period a year earlier at the 507 papers that reported circulation totals in both periods.

The drop was only 2.6 percent in the September 2007 period, compared with September 2006. In the six-month period that ended in March 2008, the decline was 3.6 percent over a year earlier, according to circulation figures that newspapers submitted to the Audit Bureau of Circulations.

Sunday circulation fell even more, 4.8 percent, to 43,631,646 in the latest period at the 571 papers with comparable totals. The drop was 3.5 percent a year ago and 4.6 percent in the period ending in March.

Newspaper circulations are declining largely because of the ongoing migration of readers to the Internet.

Despite the drops, newspapers are currently more worried about even steeper, double-digit reductions in advertising revenue caused largely by the weak economy.

Many papers have offset circulation declines with price increases, and some have purposely let some sales slide to focus on those readers who are coveted by advertisers or live in outlying areas that are more expensive to reach.

USA Today remains the nation's top-selling newspaper, with average daily circulation of 2,293,310, just 173 more than last year. The No. 2 daily, The Wall Street Journal, also reported flat circulation — up just 117 copies to 2,011,999.

The New York Times saw circulation decline 3.6 percent to 1,000,665, while the Los Angeles Times had a 5.2 percent drop to 739,147.

The other papers in the top 25 also saw circulation drops ranging from 1.9 percent at The Washington Post to 13.6 percent at The Atlanta Journal-Constitution.

The New York Times remains the top paper on Sundays, when USA Today and the Journal do not publish, with a circulation of 1,438,585, down 4.1 percent. The Los Angeles Times follows at 1,055,076, down 5.1 percent, and the Post at 866,057, a decrease of 3.2 percent.

Among the top 25, only the St. Louis Post-Dispatch and the St. Petersburg (Fla.) Times reported Sunday gains, of 0.8 percent and 0.1 percent, respectively.

Despite the industrywide decline in circulation, five papers outside the top 25 reported gains of at least 5 percent, led by the Wisconsin State Journal of Madison, where circulation rose 10.6 percent to 97,012.

The other gainers are The Macomb Daily of Mount Clemens, Mich., The Daily Sun of The Villages, Fla., The Times of Trenton, N.J., and the Citizen Tribune of Morristown, Tenn.