WASHINGTON, Jan. 1 (Xinhuanet) -- U.S. President George W. Bush on Sunday launched another strong defense for the controversial secret domestic spying program he authorized the National Security Agency (NSA) to conduct after the Sept. 11, 2001, attacks.

    The program was legal and vital to thwart terrorist attacks against the United States, Bush told journalists during a visit to soldiers wounded in Iraq at Brooke Army Medical Center in San Antonio, Texas.

    The president said the domestic surveillance project was "a limited program designed to prevent attacks" on the United States,and that "most Americans understand the need to find out what the enemy's thinking."

    The surveillance, he added, involved phone calls from outside the United States by people associated with al Qaeda. "It's seems logical to me that if we know there's a phone number associated with al Qaeda or an al Qaeda affiliate and they're making phone calls, it makes sense to find out why," he said.

    "They attacked us before, they'll attack us again," Bush noted.

    The president criticized the so far unknown source or sources who leaked information about the clandestine program to The New York Times, which first reported on the program last month.

    "The fact that somebody leaked this program causes great harm to the United States," Bush said.

    The Justice Department has launched an investigation into the leak of information about the program.

    The revelation of the program by the Times that the National Security Agency had been conducting warrantless surveillance has created a political debate in Washington, where some lawmakers from both parties have been seeking an inquiry into its legality.

    Also on Sunday, the Times reported that a top Justice Department official objected in 2004 to aspects of the NSA's domestic surveillance program and refused to sign on to its continued use amid concerns about its legality and oversight.

    The concerns prompted two of Bush's most senior aides to make an emergency visit to a Washington hospital in March 2004 to discuss the program's future and try to win the needed approval from then Attorney General John Ashcroft, who was hospitalized, the report said. Enditem