Walk-in suicide bombers like those who have attacked public places in Israel will hit the United States eventually, FBI Director Robert Mueller said.

Mueller thinks such attacks are inevitable, and we will not be able to stop them, he said in response to a question during a speech to the National Association of District Attorneys meeting in Alexandria, Va.

Mueller said the degree of fanaticism an informant must exhibit to get into the inner circle of a terrorist group makes it difficult for law enforcement agencies to penetrate such organizations and prevent such attacks.

The NYPD plans to issue roll call alerts to rank-and-file cops to be on the lookout for suicide bombers, law enforcement officials said yesterday.

And the FBI is reaching out to building owners and tenants to be on the guard for terrorism.

The moves came as the city reacted to the warning by the head of the FBI that suicide attacks are likely in the next wave of terrorist action in the U.S.

Mayor Bloomberg said vigilance would be a way of life for the foreseeable future.

Mueller's prediction follows Vice President Dick Cheney’s recent warning that because no specific information is available, the United States is finding it difficult to respond to the latest intelligence hints that al-Qaida may be planning another attack.

Mueller said law enforcement has been somewhat successful in combating acts of terrorism in Northern Ireland by developing sources who could provide information about terrorist plans and by using electronic surveillance.

But he said the difficulty of getting informants inside terrorist groups targeting the United States makes it much harder to obtain advance information.

At the prosecutors meeting, Mueller said the FBI now believes that "an al-Qaida bomb maker" constructed the shoe bomb that Richard Reid had when he was apprehended aboard a flight from Paris to the United States in December.

Mueller made the comment in describing how the FBI is increasing its recruitment of scientific experts to help in terrorism investigations and is "centralizing analytical capability" to coordinate evidence gathering.

Mueller also said the arrest of Abu Zubaydah, a top al-Qaida operative, during raids in Pakistan in March was the result of a joint FBI-CIA operation. He cited the raids as an example of how the traditional wall between the FBI and the CIA is coming down as the two agencies battle terrorism.