FBI interviews of thousands of Iraqis living in the United States have yielded valuable information about possible targets for U.S. troops in Iraq, FBI Director Robert Mueller said Thursday.

Some of the 6,700 Iraqis interviewed so far have described bunkers, tunnel systems, telecommunications networks, infrastructure, manufacturing plants and Iraqi military officials, Mueller and other U.S. law enforcement officials said.

The intelligence, sometimes only fragmentary, is matched with information collected by the CIA and Defense Department and checked for accuracy before it is used to prosecute the war, the officials said.

They declined to provide specifics, which are classified, and expressed concern that too much detail could expose cooperating Iraqis or their family members in Iraq to retaliation.

"What we have found in our interviews around the country is a wealth of information," Mueller told the House Appropriations subcommittee that oversees the FBI and Justice Department budget. "We have been gratified with the information we have received, much of it very helpful."

The FBI is working toward a goal of interviewing about 11,000 Iraqis who have traveled to Iraq recently or have ties to Iraq's military. Many of these people are highly educated, have connections to Iraq's ruling classes and oppose the regime of President Saddam Hussein, officials said.

The interviews also are aimed at learning the identities of any terrorists or Iraqi spies in this country. Mueller did not say whether any Iraqis fitting that description had been found, although officials say about 30 people have been detained on immigration violations.

Reaction from Muslim communities has been mixed, with some concerned about being singled out and others eager to help the FBI. Rep. Jose Serrano, D-N.Y., urged Mueller to be careful, citing incidents such as the mass detention of Japanese-Americans during World War II.

"How do you make sure that we don't go crazy here?" Serrano asked.

Mueller replied that FBI guidelines and training, laws passed by Congress and lawmakers' oversight are all working to ensure agents don't violate civil liberties or people's privacy. Any instances of abuse will be dealt with immediately, he said.

"If we are overstepping our bounds in the Muslim community, I want to hear about it," he said.

Mueller also said the FBI is investigating Iraq's acquisition of unmanned aircraft, which could be used against U.S. forces. Without being specific, Mueller said the FBI is working with U.S. private industry to determine how Iraq obtained the technology to build them.

"We have several ongoing investigations into that," Mueller said.

On the al-Qaida front, Mueller said the FBI has received more than 1,000 reports of possible sightings of suspected terrorist Adnan G. El Shukrijumah since issuing a worldwide alert for him last Thursday. His name came up following the March 1 capture of Khalid Shaikh Mohammed, described as the top al-Qaida operational planner.

Mueller said El Shukrijumah has "direction, the ability and the will to undertake terrorist attacks" against U.S. targets but added that El Shukrijumah is not believed to be in the United States despite having longtime ties to South Florida.

"We have our counterparts overseas looking for him," Mueller said.