The outgoing U.S. Marine Corps general in charge of western Iraq said Sunday he opposed a Marine assault on militants in the volatile city of Fallujah in April and the subsequent decision to withdraw from the city and turn over control to a security force of former Iraqi soldiers.

That security force, known as the Fallujah Brigade, was formally disbanded last week. Not only did the brigade fail to combat militants, it actively aided them, surrendering weapons, vehicles and radios to the insurgents, according to senior Marine officers. Some brigade members even participated in attacks on Marines ringing the city, the officers said.

The comments by Lt. Gen. James T. Conway, made shortly after he relinquished command of the 1st Marine Expeditionary Force on Sunday, amounted to a stinging broadside against top U.S. military and civilian leaders who ordered the Fallujah invasion and withdrawal. His statements also provided the most detailed explanation -- and justification -- of Marine actions in Fallujah this spring, which have been widely criticized for increasing insurgent activity in the city and turning it into a "no-go" zone for U.S. troops.

Conway arrived in Iraq in March pledging to accelerate reconstruction projects as a way to subdue Anbar province, dominated by Sunni Muslims. But on March 31 he was confronted in Fallujah with the killing of four U.S. security contractors, whose bodies were mutilated or burned by a celebrating mob. Conway said he resisted calls for revenge, and instead advocated targeted operations and continued engagement with municipal leaders.

"We felt like we had a method that we wanted to apply to Fallujah: that we ought to probably let the situation settle before we appeared to be attacking out of revenge," he said in an interview with four journalists after the change-of-command ceremony. "Would our system have been better? Would we have been able to bring over the people of Fallujah with our methods? You'll never know that for sure, but at the time we certainly thought so."

He echoed an argument made by many Iraqi politicians and American analysts -- that the U.S. attack further radicalized a restive city, leading many residents to support the insurgents. "When we were told to attack Fallujah, I think we certainly increased the level of animosity that existed," Conway said.

He would not say where the order to attack originated, only that he received an order from his superior at the time, Army Lt. Gen. Ricardo Sanchez, the overall commander of U.S. forces in Iraq. Some senior U.S. officials in Iraq have said the command originated in the White House.

"We follow our orders," Conway said. "We had our say, and we understood the rationale, and we saluted smartly, and we went about the attack."

The Marine assault on Fallujah in April ended abruptly after three days. Conway expressed displeasure at the order he received from Sanchez to cease offensive operations, a decision that culminated in the formation of the Fallujah Brigade.

"When you order elements of a Marine division to attack a city, you really need to understand what the consequences of that are going to be and not perhaps vacillate in the middle of something like that," he said. "Once you commit, you got to stay committed."

Noting that six Marines were killed and six wounded in those first three days, he added: "We were quite happy with the progress of the attack on the city. We thought we were sparing civilian lives everywhere and anywhere that availed itself to us. We thought we were going to be done in a few days. That's the Monday morning quarterbacking."

The Marine encirclement of Fallujah was highly controversial. Iraqi political leaders and U.N. envoy Lakhdar Brahimi accused U.S. military commanders of engaging in collective punishment of city residents.

Although the order to stop the fighting and seek another solution was made above Conway, he was responsible for placing Iraqis in charge of security. He formed the Fallujah Brigade after the head of Iraq's intelligence service, Mohammed Abdullah Shahwani, brought a handful of former Iraqi army generals to Camp Fallujah, the Marines' base. The generals offered to set up a force of more than 1,000 former soldiers from Fallujah who would control the city and combat the insurgents, including a cluster of non-Iraqi Islamic militants. In exchange, the Marines pledged to withdraw from the city.

But the brigade never developed as planned. Instead of wearing the desert camouflage uniforms the Marines provided, members dressed in their old Iraqi army fatigues. Instead of confronting insurgents, the former soldiers initially manned traffic checkpoints leading into the city. After a few weeks, even that ended.

Marine officials say they believe that threats, tribal ties and other influences led many of the soldiers to tacitly support the insurgents. The leaders of two National Guard battalions, which had been working with the Fallujah Brigade, were kidnapped. One was beheaded and the fate of the other is unknown. A video of the killing has circulated in Fallujah to dissuade people from working with security forces.

Eventually, the 800 AK-47 assault rifles, 27 pickup trucks and 50 radios the Marines gave the brigade wound up in the hands of the insurgents, according to Marine officers. Marines manning a checkpoint on the city's eastern fringe were shot at by gunmen wearing Fallujah Brigade uniforms.

Conway's chief of staff, Col. John Coleman, said he and other senior Marine officers did not foresee the challenges in getting people from Fallujah to police the city. "I'm not sure we fully understood the hardness of the city, the harshness of the elements operating inside," he said.

Conway insisted the brigade was an experiment. "The early success of the Fallujah Brigade was ultimately its downfall," he said. "You had to have a force that came from Fallujah in order for it to be accepted by the people of all. They're very xenophobic . . . but in the end those were the same things I think that dictated the demise of the Fallujah Brigade. Because they were from the local area, they were emasculated as far as their ability to do something very aggressive."

With no security forces in Fallujah now -- U.S. troops do not patrol inside the city limits -- the area has become a haven for insurgents, Marine officers said. Among the foreign-born fighters believed to be holed up in Fallujah is Abu Musab Zarqawi, a Jordanian who is alleged to have organized car bombings, kidnappings and other attacks targeting Americans and Iraqis.

Over the past week, U.S. warplanes have bombed suspected insurgent safe houses and other targets in the city. Coleman said those attacks have killed hundreds of insurgents.

Conway's successor, Lt. Gen. John F. Sattler, suggested that another incursion into the city would require not just the approval of Iraq's interim prime minister but also likely would involve the joint participation of Iraqi army units. "When we approach it next time, we will approach it a little bit differently," he said.

But Sattler said he was unwilling to tolerate an insurgent-controlled city. "The status quo," he said, "is unacceptable."

Marine Lt. Gen. James T. Conway says the U.S.-led assault on Fallujah served to increase "the level of animosity" in the city.