WASHINGTON, Sept. 20 - The Pentagon said Tuesday that it had blocked several military officers and intelligence analysts from testifying at an open Congressional hearing about a highly classified intelligence program that, the officers have said, identified a ringleader of the Sept. 11 attacks as a potential terrorist a year before the attacks.
The officers and intelligence analysts had been scheduled to testify on Wednesday about the program, known as Able Danger, at a hearing of the Senate Judiciary Committee.
Bryan Whitman, a Defense Department spokesman, said in a statement that open testimony "would not be appropriate."
"We have expressed our security concerns and believe it is simply not possible to discuss Able Danger in any great detail in an open public forum," Mr. Whitman said.
He offered no other explanation of the Pentagon's reasoning.
Senator Arlen Specter, Republican of Pennsylvania and chairman of the committee, said he was surprised by the Pentagon's decision because "so much of this has already been in the public domain, and I think that the American people need to know what happened here."
Mr. Specter said in a telephone interview that he intended to go ahead with the hearing on Wednesday and hoped that it "may produce a change of heart by the Department of Defense in answering some very basic questions."
Two military officers - an active-duty captain in the Navy and a lieutenant colonel in the Army Reserve - have recently said publicly that they were involved with Able Danger and that the program's analysts identified Mohamed Atta, the Egyptian-born ringleader of the Sept. 11 attacks, by name as a potential terrorist by early 2000.
They said they tried to share the information with the Federal Bureau of Investigation in the summer of 2000, more than a year before the attacks, but were blocked by Defense Department lawyers. F.B.I. officials, who answer to the jurisdiction of Mr. Specter's committee, have confirmed that the Defense Department abruptly canceled meetings in 2000 between the bureau's Washington field office and representatives of the Able Danger team.
The Pentagon had said that it interviewed three other people who were involved with Able Danger and who said that they, too, recalled the identification of Mr. Atta as a terrorist suspect. Mr. Specter said his staff had talked to all five of the potential witnesses and found that "credibility has been established" for all of them.
