Controversy continued yesterday over the number of participants in the Million Man March as Nation of Islam leader Louis Farrakhan pledged to sue the U.S. Park Police to force it to revise its estimate of 400,000.

Farrakhan and march organizers insisted that the rally drew more than 1 million people to the Mall.

"What would make anyone fail to give us that credit but racism, at the root of it, white supremacy?" Farrakhan said.

Park Police said yesterday that they stand by their crowd estimate, arrived at by examining aerial photographs and applying techniques used at other mass demonstrations in Washington.

"I expected we would have a controversy," said Maj. Robert H. Hines, a spokesman for the U.S. Park Police, the law enforcement agency responsible for policing the Mall. "But we think we have a reasonable and objective number." He said there was no political or ideological motivation behind the count.

In essence, the Park Police counting method involves photographing sections of the Mall, deciding how much of each section is occupied and then determining the density of the crowd occupying the sections, Hines said.

Police said they took photos of the Mall, the Capitol grounds and the surrounding streets at three different times. Measurement was made easier by low turnover in the crowd, he said, as few people left until midafternoon.

"To be a million, the crowd would have had to go all the way back to the Lincoln Memorial with thick density," Hines said. He said police also photographed buses at Robert F. Kennedy Memorial Stadium and factored in the number of people who rode Metro and came to Washington by train.

The estimates drew instant criticism, however. Sam Jordan, director of the D.C. Office of Emergency Preparedness, said he had seen only two larger crowds than Monday's event -- the 1976 Bicentennial celebration and President Clinton's inauguration. Monday's estimate "was not a good number given to you," he said.

Abdul Alim Muhammad, a march official who worked with Park Police on its count, said federal officials denied organizers' request to fly a helicopter over the event to count themselves.

"This reminds me of plantation days when we would pick 100 bales of cotton and they would give us credit for 40 bales," he said.

Despite Park Police experience at the task, Hines said his agency recognizes that estimating crowds "is not an exact science." He said estimates could err by as much as 20 percent.

The estimate of 400,000 people denoted "a very successful" demonstration, Hines said.

The crowd far exceeded such outpourings as the 270,000 for the presidential inauguration in 1993, 300,000 for an April 1989 abortion rights march and 300,000 for an April 1993 lesbian and gay rights march. The 1963 March on Washington, a landmark civil rights demonstration, drew 250,000 people. CAPTION: Million Man March organizers say more than 1 million people attended the rally, disputing the U.S. Park Police's estimate of 400,000.