Circulation at American newspapers slipped another notch over the past six months, according to an analysis of Audit Bureau of Circulations figures conducted by the Newspaper Association of America.

NAA studied ABC’s March 31, 2006 Fas-Fax report and said that daily circulation from 770 newspapers reporting dropped to 45.4 million, a 2.5 percent decrease from the 46.6 million copies sold in the same period a year ago. On Sunday, average circulation for 610 newspapers reporting declined 3.1 percent, to 48.5 million.

The San Francisco Chronicle reported the most significant drop, shedding 15 percent of its circulation to 398,246 copies. The Boston Globe’s circulation, meantime, fell more than 8 percent.

The NAA attempted to tone down the ABC report, citing research that shows that circulation only represents about a third of a typical newspaper’s total audience.

“Both circulation and readership are important, valid measures of the newspaper audience, but counting only the number of units sold on a given day obscures the actual use of newspapers and consumer exposure to advertising,” said NAA President and Chief Executive Officer John F. Sturm.

According to the group’s Web research, the online audience for newspapers hit record levels in the first quarter of 2006, with more than one in three of all Internet users visiting a newspaper Web site over the course of a month.