WASHINGTON - The Central Intelligence Agency in 2004 hired outside contractors from the private security contractor Blackwater USA as part of a secret program to locate and assassinate top operatives of Al Qaeda, according to current and former government officials.

Leon E. Panetta, the director of the Central Intelligence Agency, canceled a program to locate and kill the leaders of Al Qaeda. (Stephen Crowley/The New York Times) Executives from Blackwater, which has generated controversy because of its aggressive tactics in Iraq, helped the spy agency with planning, training and surveillance. The C.I.A. spent several million dollars on the program, which did not successfully capture or kill any terrorist suspects.

The fact that the C.I.A. used an outside company for the program was a major reason that Leon E. Panetta, the C.I.A.'s director, became alarmed and called an emergency meeting in June to tell Congress that the agency had withheld details of the program for seven years, the officials said.

It is unclear whether the C.I.A. had planned to use the contractors to actually capture or kill Qaeda operatives, or just to help with training and surveillance in the program. American spy agencies have in recent years outsourced some highly controversial work, including the interrogation of prisoners. But government officials said that bringing outsiders into a program with lethal authority raised deep concerns about accountability in covert operations.

Officials said the C.I.A. did not have a formal contract with Blackwater for this program but instead had individual agreements with top company officials, including the founder, Erik D. Prince, a politically connected former member of the Navy Seals and the heir to a family fortune. Blackwater's work on the program actually ended years before Mr. Panetta took over the agency, after senior C.I.A. officials themselves questioned the wisdom of using outsiders in a targeted killing program.

Blackwater, which has changed its name, most recently to Xe Services, and is based in North Carolina, in recent years has received millions of dollars in government contracts, growing so large that the Bush administration said it was a necessary part of its war operation in Iraq.

It has also drawn controversy. Blackwater employees hired to guard American diplomats in Iraq were accused of using excessive force on several occasions, including shootings in Baghdad in 2007 in which 17 civilians were killed. Iraqi officials have since refused to give the company an operating license.

Several current and former government officials interviewed for this article spoke only on the condition of anonymity because they were discussing details of a still classified program.

Paul Gimigliano, a C.I.A. spokesman, declined to provide details about the canceled program, but he said that Mr. Panetta's decision on the assassination program was "clear and straightforward."

"Director Panetta thought this effort should be briefed to Congress, and he did so," Mr. Gimigliano said. "He also knew it hadn't been successful, so he ended it."

A Xe spokeswoman did not return calls seeking comment.

Senator Dianne Feinstein, the California Democrat who leads the Senate Intelligence Committee, also declined to give details of the program. But she praised Mr. Panetta for notifying Congress. "It is too easy to contract out work that you don't want to accept responsibility for," she said.

The C.I.A. this summer conducted an internal review of the assassination program that recently was presented to the White House and the Congressional intelligence committees. The officials said that the review stated that Mr. Panetta's predecessors did not believe that they needed to tell Congress because the program was not far enough developed.

The House Intelligence Committee is investigating why lawmakers were never told about the program. According to current and former government officials, former Vice President Dick Cheney told C.I.A. officers in 2002 that the spy agency did not need to inform Congress because the agency already had legal authority to kill Qaeda leaders.

One official familiar with the matter said that Mr. Panetta did not tell lawmakers that he believed that the C.I.A. had broken the law by withholding details about the program from Congress. Rather, the official said, Mr. Panetta said he believed that the program had moved beyond a planning stage and deserved Congressional scrutiny.

"It's wrong to think this counterterrorism program was confined to briefing slides or doodles on a cafeteria napkin," the official said. "It went well beyond that."

Current and former government officials said that the C.I.A.'s efforts to use paramilitary hit teams to kill Qaeda operatives ran into logistical, legal and diplomatic hurdles almost from the outset. These efforts had been run by the C.I.A.'s counterterrorism center, which runs operations against Al Qaeda and other terrorist networks.

In 2002, Blackwater won a classified contract to provide security for the C.I.A. station in Kabul, Afghanistan, and the company maintains other classified contracts with the C.I.A., current and former officials said.

Over the years, Blackwater has hired several former top C.I.A. officials, including Cofer Black, who ran the C.I.A. counterterrorism center immediately after the Sept. 11 attacks.

C.I.A. operatives also regularly use the company's training complex in North Carolina. The complex includes a shooting range used for sniper training.

An executive order signed by President Gerald R. Ford in 1976 barred the C.I.A. from carrying out assassinations, a direct response to revelations that the C.I.A. had initiated assassination plots against Fidel Castro of Cuba and other foreign politicians.

The Bush administration took the position that killing members of Al Qaeda, a terrorist group that attacked the United States and has pledged to attack it again, was no different from killing enemy soldiers in battle, and that therefore the agency was not constrained by the assassination ban.

But former intelligence officials said that employing private contractors to help hunt Qaeda operatives would pose significant legal and diplomatic risks, and they might not be protected in the same way government employees are.

Some Congressional Democrats have hinted that the program was just one of many that the Bush administration hid from Congressional scrutiny and have used the episode as a justification to delve deeper into other Bush-era counterterrorism programs.

But Republicans have criticized Mr. Panetta's decision to cancel the program, saying he created a tempest in a teapot.

"I think there was a little more drama and intrigue than was warranted," said Representative Peter Hoekstra of Michigan, the top Republican on the House Intelligence Committee.

Officials said that the C.I.A. program was devised partly as an alternative to missile strikes using drone aircraft, which have accidentally killed civilians and cannot be used in urban areas where some terrorists hide.

Yet with most top Qaeda operatives believed to be hiding in the remote mountains of Pakistan, the drones have remained the C.I.A.'s weapon of choice. Like the Bush administration, the Obama administration has embraced the drone campaign because it presents a less risky option than sending paramilitary teams into Pakistan.