WASHINGTON - President Bush personally blocked a Justice Department investigation of the anti-terror eavesdropping program that intercepts Americans' international calls and e-mails, Attorney General Alberto Gonzales said Tuesday.

Bush refused to grant security clearances for department investigators who were looking into the role Justice lawyers played in crafting the program, under which the National Security Agency listens in on telephone calls and reads e-mail without court approval, Gonzales told the Senate Judiciary Committee.

Without access to the sensitive program, the department's Office of Professional Responsibility closed its investigation in April.

"It was highly classified, very important and many other lawyers had access. Why not OPR?" Sen. Arlen Specter, R-Pa., the committee chairman, asked Gonzales.

"The president of the United States makes the decision," Gonzales replied.

Later, at the White House, spokesman Tony Snow said senior officials, including Gonzales, review the eavesdropping program every 45 days. The president did not consider the Justice unit that functions as a legal ethics watchdog to be the "proper venue," Snow said.

"What he was saying is that in the case of a highly classified program, you need to keep the number of people exposed to it tight for reasons of national security, and that's what he did," Snow said.

Yet, according to OPR chief Marshall Jarrett, "a large team" of prosecutors and FBI agents were granted security clearances to pursue an investigation into leaks of information that resulted in the program's disclosure in December.

Justice Department Inspector General Glenn A. Fine and two of his aides were among other department officials who were granted clearances, Jarrett said in an April memo explaining the end of his probe. That memo was released by the Justice Department on Tuesday.

The inspector general is conducting a limited, preliminary inquiry into the FBI's role in and use of information from the NSA surveillance program, Deputy Inspector General Paul Martin said.

The existence of the eavesdropping program outraged Democrats, civil libertarians and even some Republicans who said Bush overstepped his authority.

A group of 13 prominent legal experts wrote lawmakers last week that the Supreme Court's recent decision striking down military commissions for detainees at the Guantanamo naval base in Cuba "strongly supports the conclusion that the president's NSA surveillance program is illegal."

Rep. Maurice Hinchey, D-N.Y., who requested the Justice Department investigation, said he and other lawmakers were preparing a letter to Bush asking him to allow the probe to go forward.

"We can't have a president acting in a dictatorial fashion," Hinchey said.

Gonzales insisted Tuesday that the president "has the inherent authority under the Constitution to engage in electronic surveillance without a warrant."

Still last week, under a deal with Specter, Bush agreed conditionally to a court review of the warrantless eavesdropping operations.

In the House, Rep. Heather Wilson, R-N.M., introduced a bill Tuesday to update the 26-year-old Foreign Intelligence Surveillance Act that would include allowing the government to monitor the suspected terrorists' communications without a court order for up to 45 days after an attack.