WASHINGTON -- The CIA spent at least $1 million on the secret intelligence proposal that aimed to develop hit squads to kill Al Qaeda leaders but never went beyond the planning stage, a congressional official said Tuesday.

The highly classified proposal, which never became operational but remained in existence until it was shut down by CIA Director Leon Panetta in June, is expected to trigger a congressional investigation, other officials said.

The House Intelligence Committee asked the CIA to provide documents about the now-canceled proposal to kill Al Qaeda leaders, and agency officials said it would comply with the request, congressional officials said Tuesday.

According to one official, the agency spent at least $1 million over the eight years that the CIA considered launching the hit teams. The official would not detail the exact amount or its uses. The official and others spoke on condition of anonymity because they were not authorized to discuss the matter publicly.

The House request for documents is likely a precursor to what would likely become a full-blown investigation into the secret operation and why the program was not disclosed to Congress. Panetta, meanwhile, has ordered a thorough internal review of the program, agency spokesman George Little said.

The House Intelligence Committee will try to establish how much was spent on the effort, whether any training was conducted and whether any officials traveled in association with the program, a committee official said. Those factors would determine whether the program had progressed enough to warrant congressional notification, the official said.

House Intelligence Committee Chairman Silvestre Reyes, D-Texas, is expected to decide as early as this week whether to press ahead with a full investigation into the CIA operation.

Panetta told Congress on June 24 that he had canceled the effort to kill Al Qaeda leaders with hit teams soon after learning about the operation. Panetta also told lawmakers that former Vice President Dick Cheney directed the CIA not to inform Congress of the specifics of the secret program.

President George W. Bush authorized the killing of Al Qaeda leaders in 2001. Congress was aware of that notification.

A congressional official said the secret CIA program was meant to carry out ground attacks with hit teams. Most attempts to kill Al Qaeda's leaders, believed to be hiding in Pakistan's troubled western border region, have used armed drone aircraft because it is difficult terrain controlled by sometimes hostile tribes. But those strikes have sometimes killed and injured innocent civilians and caused outrage in Pakistan.

Sen. Russ Feingold, D-Wis., said Monday that the CIA's failure to brief Congress violated the law.

Rep. Peter Hoekstra, R-Mich., the senior GOP member of the committee, said he would support an investigation. But from what he knows now, Hoekstra said, he does not believe the effort merited congressional notification.

Like many other Republicans, Hoekstra believes the Democratic anger about not being notified of the program sooner is meant to bolster House Speaker Nancy Pelosi, who came under an avalanche of GOP criticism in May for saying she believes the CIA lied to her about its harsh interrogation program in 2002.

The House has delayed floor debate on an intelligence bill that would require the president to expand the number of members of Congress briefed on covert operations; that is, secret missions undertaken in foreign countries to affect their political, military or economic situation.

The White House has threatened to veto that bill if it includes the notification requirement. Current law allows the president to notify top members in the House and Senate and on the intelligence committees on the most sensitive operations.