In the aftermath of Sept. 11, Arab-Americans have a greater fear of racial profiling and immigration enforcement than of falling victim to hate crimes, according to a national study financed by the Justice Department.

The study also concluded that local police officers and federal agents were straining under the pressure to fight terrorism, and that new federal policies in this effort were poorly defined and inconsistently applied.

The two-year study, released today by the Vera Institute of Justice, explored the changed relationship between Arab-Americans and law enforcement in the years since the 2001 terrorist attacks. The Vera Institute is a nonprofit policy research center based in New York.

About 100 Arab-Americans and 111 law enforcement personnel, both F.B.I. agents and police officers, participated in the study, which was conducted from 2003 to 2005. Some respondents were interviewed privately and others took part in focus groups in cities around the nation, which were not identified in order to protect the identities of the respondents.

Both Arab-American community leaders and law enforcement officials interviewed in the study said that cooperation between both groups had suffered from a lack of trust.

“It underscores the importance of community policing, of engaging the Arab and Muslim community in a constructive way and bringing them in to be partners,” said Farhana Khera, the executive director of Muslim Advocates, a national nonprofit organization of lawyers.

While Muslims represent a spectrum of ethnic and national backgrounds, the study focused on Arab-Americans in order to understand the experience of one group more deeply, said Nicole Henderson, the lead author of the report. An estimated two-thirds of Arab-Americans are Christian.

Arab-Americans reported an increasing sense of victimization, suspicion of government and law enforcement, and concerns about protecting their civil liberties, according to the study, which was paid for by the National Institute of Justice, a research agency of the Justice Department.

A fear of surveillance ranked high among their concerns. During one focus group, a woman told the story of an encyclopedia salesman who came to her door and asked to use the bathroom. She worried that he might have been an agent trying to plant a listening device in her home.

While hate crimes against Arab-Americans spiked after Sept. 11, they have decreased in the years since, according to both law enforcement and Arab-American respondents.

A series of post-9/11 policies have sown the deepest fear among Arab-Americans, including unease about the USA Patriot Act, voluntary interviews of thousands of Arab-Americans by federal agents, and an initiative known as Special Registration, in which more than 80,000 immigrant men were fingerprinted, photographed and questioned by authorities.

These new measures threatened to harm decades of work by police departments to build trust in their communities, especially among immigrants, the study concluded. After 9/11, federal agents increasingly turned to the police for help with gathering intelligence and enforcing immigration laws, Ms. Henderson said.

F.B.I. agents were also given expanded powers to arrest people for immigration violations in connection with terrorism cases.

The study concluded that there was confusion among both F.B.I. agents and the local police about their roles in enforcing immigration, and that their resources had been stretched thin by counterterrorism initiatives.

John Miller, an assistant director for the Federal Bureau of Investigation, said the report confirmed many of the realities facing the bureau.

“We have finite resources and tremendous responsibilities,” Mr. Miller said. “When you take 40 percent of your resources and turn them towards national security issues in the wake of Sept. 11 because of a significant and demonstrable threat, you’re going to see a strain on resources.”

The degree to which police officers have enforced immigration laws varied, according to the study: Some departments formally deputized officers to arrest people for immigration violations, while other departments left this to the discretion of officers.

Both Arab-Americans and law enforcement personnel expressed dismay about the reporting of false information in the form of anonymous tips. F.B.I. agents said they had responded to calls stemming from petty disputes, business competition and dating rivalries, according to the study.

“It reminds me of Syria,” an Arab-American was quoted as saying in the study. “If someone wants to get you, they will call the police.”

Both Arab-Americans and law enforcement respondents acknowledged that the relationship between them was necessary, but could be improved.

Mr. Miller said the process would take time.

“We didn’t bring this on the community — the terrorists did,” he said. “The community is paying for that. We are paying for that as law enforcement because when we’re doing our investigations, it seems like we’re singling out a group or a religion and the fact is, we’re not. We have to go where the leads take us.”

In the weeks after Sept. 11, community outreach by the Los Angeles County Sheriff’s Department helped engender trust among Muslims, said Sheriff Lee Baca. The department received reports that Pakistani immigrants working at 7-Eleven stores had been harassed. In response, officers visited more than 100 stores in Los Angeles and Orange Counties, he said.

“Our premise here in Los Angeles is that unless we enlist Muslim-American partnerships in the homeland security mission, we are leaving out our greatest resource for preventing terrorist attacks,” Sheriff Baca said.

The Vera Institute study concluded that Arab-Americans tended to have a closer relationship with the local police than with federal agents.

James Zogby, president of the Arab American Institute in Washington, said increased surveillance by the F.B.I. had damaged the image many Arab-Americans had of the bureau.

“I think there’s more of an arm’s length attitude,” Mr. Zogby said. “The community still wants very much to cooperate because we know it is important and good to do so, but the cooperation is a one-way street.

“It’s, ‘Tell us everything you know,’ which in most cases is nothing,” he said. “What we want is more of relationship, a partnership, and not to be viewed as just sources.”