WASHINGTON, Aug. 23 - The Bush administration is replacing the director of a small but critical branch of the Justice Department, months after he complained that senior political officials at the department were seeking to play down newly compiled data on the aggressive police treatment of black and Hispanic drivers.

The demotion of the official, Lawrence A. Greenfeld, whom President Bush named in 2001 to lead the Bureau of Justice Statistics, caps more than three years of simmering tensions over charges of political interference at the agency. And it has stirred anger and tumult among many Justice Department statisticians, who say their independence in analyzing important law enforcement data has been compromised.

Officials at the White House and the Justice Department said no political pressure had been exerted over the statistics branch. But they declined to discuss the job status of Mr. Greenfeld, who told his staff several weeks ago that he had been asked to move on after 23 years of generally high marks as a statistician and supervisor at the agency. Mr. Greenfeld, who was initially threatened with dismissal and the possible loss of some pension benefits, is expected to leave the agency soon for a lesser position at another agency.

With some 50 employees, the Bureau of Justice Statistics is a low-profile agency within the sprawling Justice Department. But it produces dozens of reports a year on issues like crime patterns, drug use, police tactics and prison populations and is widely cited by law enforcement officials, policy makers, social scientists and the news media. Located in an office separate from the Justice Department, it strives to be largely independent to avoid any taint of political influence.

The flashpoint in the tensions between Mr. Greenfeld and his political supervisors came four months ago, when statisticians at the agency were preparing to announce the results of a major study on traffic stops and racial profiling, which found disparities in how racial groups were treated once they were stopped by the police.

Political supervisors within the Office of Justice Programs ordered Mr. Greenfeld to delete certain references to the disparities from a news release that was drafted to announce the findings, according to more than a half-dozen Justice Department officials with knowledge of the situation. The officials, most of whom said they were supporters of Mr. Greenfeld, spoke on condition of anonymity because they were not authorized to discuss personnel matters.

Mr. Greenfeld refused to delete the racial references, arguing to his supervisors that the omissions would make the public announcement incomplete and misleading. Instead, the Justice Department opted not to issue a news release on the findings and posted the report online.

Some statisticians said that decision all but assured the report would get lost amid the avalanche of studies issued by the government. A computer search of news articles found no mentions of the study.

Congressional opponents of racial profiling, who have criticized what they see as an ambivalent stance on the issue by the Bush administration, said they were frustrated to learn that the Justice Department had completed the Congressionally mandated study without announcing its findings or briefing members of Congress on it. They accused the Justice Department of effectively burying the findings to play down new data that would add grist to the debate over using racial and ethnic data in law enforcement and terrorism investigations.

"My suspicions always go up if a report like this is just deep-sixed," said Representative John Conyers Jr., Democrat of Michigan, who is dean of the Congressional Black Caucus and plans to introduce legislation this fall that would ban the use of racial or ethnic police profiling.

The April study by the Justice Department, based on interviews with 80,000 people in 2002, found that white, black and Hispanic drivers nationwide were stopped by the police that year at about the same rate, roughly 9 percent. But, in findings that were more detailed than past studies on the topic, the Justice Department report also found that what happened once the police made a stop differed markedly depending on race and ethnicity.

Once they were stopped, Hispanic drivers were searched or had their vehicles searched by the police 11.4 percent of the time and blacks 10.2 percent of the time, compared with 3.5 percent for white drivers. Blacks and Hispanics were also subjected to force or the threat of force more often than whites, and the police were much more likely to issue tickets to Hispanics rather than simply giving them a warning, the study found.

The authors of the study said they were not able to draw any conclusions about the reason for the differing rates, but they said the gaps were notable. The research "uncovered evidence of black drivers having worse experiences - more likely to be arrested, more likely to be searched, more likely to be have force used against them - during traffic stops than white drivers," the report concluded.

In April, as the report was being completed, Mr. Greenfeld's office drafted a news release to announce the findings and submitted it for review to the office of Tracy A. Henke, who was then the acting assistant attorney general who oversaw the statistics branch.

The planned announcement noted that the rate at which whites, blacks and Hispanics were stopped was "about the same," and that finding was left intact by Ms. Henke's office, according to a copy of the draft obtained by The New York Times.

But the references in the draft to higher rates of searches and use of force for blacks and Hispanics were crossed out by hand, with a notation in the margin that read, "Do we need this?" A note affixed to the edited draft, which the officials said was written by Ms. Henke, read "Make the changes," and it was signed "Tracy." That led to a fierce dispute after Mr. Greenfeld refused to delete the references, officials said.

Ms. Henke, who was nominated by Mr. Bush last month to a senior position at the Department of Homeland Security, said in a brief telephone interview that she did not recall the episode.

Brian Rohrkasse, a spokesman for the Justice Department, declined to discuss Mr. Greenfeld's job status, citing confidential personnel matters, but said that "there was no effort to suppress information since the report was released in its entirety." Mr. Rohrkasse said the department had also posted on its Web site a number of other statistical reports without issuing news releases.

Mr. Greenfeld declined to discuss the handling of the traffic report or his departure from the statistics agency. But he emphasized in an interview that his agency's data had never been changed because of political pressure and added that "all our statistics are produced under the highest quality standards."

As a political appointee named to his post by Mr. Bush in 2001, "I serve at the pleasure of the president and can be replaced at any time," Mr. Greenfeld said. "There's always a natural and healthy tension between the people who make the policy and the people who do the statistics. That's there every day of the week, because some days you're going to have good news, and some days you're going to have bad news."

When asked if those political pressures had grown worse for his agency lately, as many of his employees asserted in interviews, he said: "I don't want to comment on that. It's just a fact of life."

Disputes between statisticians and policy makers at the Justice Department have flared occasionally over the years, particularly over the question of what credit if any the administration in power could take for dips in national crime rates. But a senior statistician, also speaking on condition of anonymity, said that "in this administration, those tensions have been even greater, and the struggles have been harder."

Another veteran statistician said: "Larry wanted to ensure that the integrity of the data was not compromised, and that's what's causing a lot of anxiety. We've seen a desire for more control over B.J.S. from the powers that be, and that's what seemed to get Larry in trouble."

Amid the debate over the traffic stop study, Mr. Greenfeld was called to the office of Robert D. McCallum Jr., then the third-ranking Justice Department official, and questioned about his handling of the matter, people involved in the episode said. Some weeks later, he was called to the White House, where personnel officials told him he was being replaced as director and was urged to resign, six months before he was scheduled to retire with full pension benefits, the officials said.

After Mr. Greenfeld invoked his right as a former senior executive to move to a lesser position, the administration agreed to allow him to seek another job, and he is likely to be detailed to the Bureau of Prisons, the officials said.

The administration has already offered the director's job at the statistics agency to a former official there, Joseph M. Bessette, but he turned it down, officials said. In an interview, Mr. Bessette declined to discuss his conversations with the administration but was quick to praise Mr. Greenfeld's work.

"I've never met a finer public servant," Mr. Bessette said, "and I think the agency has been taken to new heights by Larry."

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