The FBI has interviewed more than 5,000 Iraqis who live in the United States and has detained around 30 since war began with Iraq, officials said Monday.

The purpose of the interviews, which the FBI says are voluntary, is to gain intelligence about the Iraqi government and military and to learn the identities of any spies or terrorists in the United States, the agency says. The FBI says it is also seeking to assure U.S. Muslims that hate crimes against them will be vigorously investigated.

Although the FBI says it is not using the interviews to arrest large numbers of Iraqis, two law enforcement officials said about 30 have been detained on immigration charges since the program began last week.

Late last month, Attorney General John Ashcroft gave the FBI and U.S. marshals authority to arrest people on immigration charges.

Some of those held are people the FBI had under surveillance and decided to apprehend when hostilities with Iraq began, the officials said. None had been charged with any terrorist plot, espionage or any other criminal offenses, the officials said.

The interviews are part of a sweeping FBI wartime effort to prevent possible reprisal acts of terrorism by Iraqi agents or Al -Qaeda operatives. The FBI also continues to search worldwide for a Saudi-born man with ties to the Miami area, Adnan G. El Shukrijumah, 27, who is suspected of plotting Al Qaeda attacks against U.S. interests.

Meanwhile, the Homeland Security Department on Monday reissued an FBI bulletin that warns police and other security officials to watch for possible indicators of Al Qaeda surveillance: hidden cameras, operatives posing as homeless people, artists or tourists, or use of scooters, bicycles cars and trucks.

Officials are urged to watch for anyone displaying unusual interest in security measures or perimeters such as fences or walls and any increase in anonymous telephone or e-mail threats, which could be a way of testing the reaction of security personnel.

By the end of this week, the FBI figures to complete its initial plan to interview 11,000 Iraqis living in the United States. These people were selected for immediate attention from a larger list of about 50,000 because they had recently traveled to Iraq or had ties to the Iraqi military, officials said.

The interviews are expected to continue at a slower pace after that priority group is finished. FBI officials say the interviews often provide them with new names that will require follow-up.

The interviews have received a mixed reception from Muslim communities around the country. Many people say they want to help the United States in its campaign against the Iraqi regime of Saddam Hussein but are concerned about being singled out for scrutiny.

"You don't have to be mistreated to be intimidated," said Ibrahim Hooper, spokesman for the Council on American-Islamic Relations. "If the FBI shows up at your place of work or talks to your neighbors, that's very intimidating."