The San Francisco Chronicle said high-resolution aerial photographs commissioned by the newspaper showed that around 65,000 people took part in last Sunday's march through downtown rather than the 200,000 announced originally.
Media reports in the aftermath of last weekend's marches around the world declared that the large crowds at the anti-war rallies indicated tangible opposition to a war in Iraq.
Rally organizers disputed the Chronicle's findings as did police officials.
"I can tell you for a fact that's an enormously low number," declared Deputy Police Chief Greg Suhr, who commanded the officers assigned to the march.
Suhr said that the 200,000 figure was his personal estimate and that no one else in the SFPD had been assigned to count heads. He said, however, that the crowd was much larger than those seen during baseball games at Pacific Bell Park, which is often filled to capacity.
"(Pacific Bell Park), just in the stands, holds 40,000," Suhr said. "The crowd at Pac Bell would pale in comparison to the crowd on Sunday."
Bill Hackwell, a spokesman for the anti-war group International ANSWER, called the Chronicle's figure "ridiculous."
The Chronicle said Friday that its estimate was based on photos taken at the time the crowd at Civic Center Plaza was at its height, and they checked their numbers against ridership figures from rapid transit systems serving downtown.
The Bay Area Rapid Transit System determined that 66,250 exited at the four downtown stations closest to the rally on Sunday between 8 a.m. and midnight, around 43,000 more than the number of downtown passengers last Sunday.
The Muni bus system and the Larkspur ferry from Marin County also reported higher ridership, the newspaper said.