As the toll of mayhem inspired by terrorist leader Abu Musab al-Zarqawi mounts in Iraq, some former officials and military officers increasingly wonder whether the Bush administration made a mistake months before the start of the war by stopping the military from attacking his camp in the northeastern part of that country.

The Pentagon drew up detailed plans in June 2002, giving the administration a series of options for a military strike on the camp Mr. Zarqawi was running then in remote northeastern Iraq, according to generals who were involved directly in planning the attack and several former White House staffers. They said the camp, near the town of Khurmal, was known to contain Mr. Zarqawi and his supporters as well as al Qaeda fighters, all of whom had fled from Afghanistan. Intelligence indicated the camp was training recruits and making poisons for attacks against the West.

Senior Pentagon officials who were involved in planning the attack said that even by spring 2002 Mr. Zarqawi had been identified as a significant terrorist target, based in part on intelligence that the camp he earlier ran in Afghanistan had been attempting to make chemical weapons, and because he was known as the head of a group that was plotting, and training for, attacks against the West. He already was identified as the ringleader in several failed terrorist plots against Israeli and European targets. In addition, by late 2002, while the White House still was deliberating over attacking the camp, Mr. Zarqawi was known to have been behind the October 2002 assassination of a senior American diplomat in Amman, Jordan.

But the raid on Mr. Zarqawi didn't take place. Months passed with no approval of the plan from the White House, until word came down just weeks before the March 19, 2003, start of the Iraq war that Mr. Bush had rejected any strike on the camp until after an official outbreak of hostilities with Iraq. Ultimately, the camp was hit just after the invasion of Iraq began.

Lisa Gordon-Hagerty, who was in the White House as the National Security Council's director for combatting terrorism at the time, said an NSC working group, led by the Defense Department, had been in charge of reviewing the plans to target the camp. She said the camp was "definitely a stronghold, and we knew that certain individuals were there including Zarqawi." Ms. Gordon-Hagerty said she wasn't part of the working group and never learned the reason why the camp wasn't hit. But she said that much later, when reports surfaced that Mr. Zarqawi was behind a series of bloody attacks in Iraq, she said "I remember my response," adding, "I said why didn't we get that ['son of a b-'] when we could."

Administration officials say the attack was set aside for a variety of reasons, including uncertain intelligence reports on Mr. Zarqawi's whereabouts and the difficulties of hitting him within a large complex.

"Because there was never any real-time, actionable intelligence that placed Zarqawi at Khurmal, action taken against the facility would have been ineffective," said Jim Wilkinson, a spokesman for the NSC. "It was more effective to deal with the facility as part of the broader strategy, and in fact, the facility was destroyed early in the war."

Another factor, though, was fear that a strike on the camp could stir up opposition while the administration was trying to build an international coalition to launch an invasion of Iraq. Lawrence Di Rita, the Pentagon's chief spokesman, said in an interview that the reasons for not striking included "the president's decision to engage the international community on Iraq." Mr. Di Rita said the camp was of interest only because it was believed to be producing chemical weapons. He also cited several potential logistical problems in planning a strike, such as getting enough ground troops into the area, and the camp's large size.

Still, after the defeat of the Taliban in Afghanistan, President Bush had said he relentlessly would pursue and attack fleeing al Qaeda fighters regardless of where they went to hide. Mr. Bush also had decided upon a policy of pre-emptive strikes, in which the U.S. wouldn't wait to be struck before hitting enemies who posed a threat. An attack on Mr. Zarqawi would have amounted to such a pre-emptive strike. The story of the debate over his camp shows how difficult the policy can be to carry out; Mr. Zarqawi's subsequent resurgence highlights that while pre-emptive strikes entail considerable risks, the risk of not making them can be significant too, a factor that may weigh in future decisions on when to attack terrorist leaders.

Some former officials said the intelligence on Mr. Zarqawi's whereabouts was sound. In addition, retired Gen. John M. Keane, the U.S. Army's vice chief of staff when the strike was considered, said that because the camp was isolated in the thinly populated, mountainous borderlands of northeastern Iraq, the risk of collateral damage was minimal. Former military officials said that adding to the target's allure was intelligence indicating that Mr. Zarqawi himself was in the camp at the time. A strike at the camp, they believed, meant at least a chance of killing or incapacitating him.

Gen. Keane characterized the camp "as one of the best targets we ever had," and questioned the decision not to attack it. When the U.S. did strike the camp a day after the war started, Mr. Zarqawi, many of his followers and Kurdish extremists belonging to his organization already had fled, people involved with intelligence say.

In recent months, Mr. Zarqawi's group has been blamed for a series of beheadings of foreigners and deadly car bombings in Iraq, as well as the recent kidnapping of Margaret Hassan, the director of CARE International there. According to wire-service reports, Mr. Zarqawi's group, recently renamed the Al Qaeda Organization for Holy War in Iraq, on Sunday claimed responsibility for the massacre of more than 40 Iraqi army recruits in eastern Iraq.

The U.S. military over the weekend announced it arrested what it said was a newly promoted senior leader in Mr. Zarqawi's group. The man's name wasn't released.

Targeting of the camp and Mr. Zarqawi before the war first was reported in an NBC Nightly News item in March, but administration officials subsequently denied it, and the report didn't give details of the planning of the attack and deliberations over it.

According to those who were involved during 2002 in planning an attack, the impetus came from Central Intelligence Agency reports that al Qaeda fighters were in the camp and that preparations and training were under way there for attacks on Western interests. Under the aegis of the Joint Chiefs of Staff, tentative plans were drawn up and sent to the White House in the last week of June 2002. Officials involved in planning had expected a swift decision, but they said they were surprised when weeks went by with no response from the White House.

Then, in midsummer, word somehow leaked out in the Turkish press that the U.S. was considering targeting the camp, and intelligence reports showed that Mr. Zarqawi's group had fled the camp. But the CIA reported that around the end of 2002 the group had reoccupied the camp. The military's plans for hitting it quickly were revived.

Gen. Tommy Franks, who was commander of the U.S. Central Command and who lately has been campaigning on behalf of Mr. Bush, suggests in his recently published memoir, "American Soldier," that Mr. Zarqawi was known to have been in the camp during the months before the war. Gen. Franks declined to be interviewed or answer written questions for this article. In referring to several camps in northern Iraq occupied by al Qaeda fighters who had fled Afghanistan after the fall of the Taliban, Gen. Franks wrote: "These camps were examples of the terrorist 'harbors' that President Bush had vowed to crush. One known terrorist, a Jordanian-born Palestinian named Abu Musab Zarqawi who had joined al Qaeda in Afghanistan -- where he specialized in developing chemical and biological weapons -- was now confirmed to operate from one of the camps in Iraq." Gen. Franks's book doesn't mention the plans to target the camp.

Questions about whether the U.S. missed an opportunity to take out Mr. Zarqawi have been enhanced recently by a CIA report on Mr. Zarqawi, commissioned by Vice President Dick Cheney. Individuals who have been briefed on the report's contents say it specifically cites evidence that Mr. Zarqawi was in the camp during those prewar months. They said the CIA's conclusion was based in part on a review of electronic intercepts, which show that Mr. Zarqawi was using a satellite telephone to discuss matters relating to the camp, and that the intercepts indicated the probability that the calls were being made from inside the camp.

--David S. Cloud contributed to this article.

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