WASHINGTON — The Bush administration built an unprecedented surveillance operation to pull in mountains of information far beyond the warrantless wiretapping previously acknowledged, a team of federal inspectors general reported Friday, questioning the legal basis for the effort but shielding almost all details on grounds they’re still too secret to reveal.

The report, compiled by five inspectors general, refers to “unprecedented collection activities” by U.S. intelligence agencies under an executive order signed by President George W. Bush after the Sept. 11, 2001, terror attacks.

Just what those activities involved remains classified, but the IGs pointedly say that any continued use of the secret programs must be “carefully monitored.”

The report says too few relevant officials knew of the size and depth of the program, let alone signed off on it. They particularly criticize John Yoo, a deputy assistant attorney general who wrote legal memos undergirding the policy. His boss, Attorney General John Ashcroft, was not aware until March 2004 of the exact nature of the intelligence operations beyond wiretapping that he had been approving for the previous two and a half years, the report says.

Most of the intelligence leads generated under what was known as the “President’s Surveillance Program” did not have any connection to terrorism, the report said.

The inspectors general interviewed more than 200 people inside and outside the government, but five former Bush administration officials refused to be questioned. They were Ashcroft, Yoo, former CIA Director George Tenet, former White House Chief of Staff Andrew Card and David Addington, an aide to former Vice President Dick Cheney.

According to the report, Addington could personally decide who in the administration was allowed access to the classified program.

Although the report documents Bush administration policies, its fallout could be a problem for the Obama administration if it inherited any or all of the still-classified operations.

Bush started the warrantless wiretapping program under the authority of a secret court in 2006, and Congress authorized most of the intercepts in a 2008 electronic surveillance law. The fate of the remaining and still classified aspects of the wider surveillance program is not clear.

The report’s revelations came the same day that House Democrats said that CIA Director Leon Panetta had ordered one eight-year-old classified program shut down after learning lawmakers had never been apprised of its existence.

The IG report said that President Bush signed off on both the warrantless wiretapping and other top-secret operations shortly after Sept. 11 in a single presidential authorization.

The report questioned the legal advice used by Bush to set up the program, pinpointing omissions and questionable legal memos written by Yoo, in the Justice Department’s Office of Legal Counsel.

The report says Yoo’s analysis approving the program ignored a law designed to restrict the government’s authority to conduct electronic surveillance during wartime, and did so without fully notifying Congress. And it said flaws in Yoo’s memos later presented “a serious impediment” to recertifying the program.

Yoo insisted that the president’s wiretapping program had only to comply with Fourth Amendment protections against search and seizure — but the report said Yoo ignored the Federal Intelligence Surveillance Act, which had previously overseen federal national security surveillance.

“The notion that basically one person at the Justice Department, John Yoo, and Hayden and the vice president’s office were running a program around the laws that Congress passed, including a reinterpretation of the Fourth Amendment, is mind boggling,” said Rep. Jane Harman, D-Calif.