From the porthole of his bunker just outside the city, U.S. Marine Capt. Jeff Stevenson could see no more than the first few rows of brick-and-concrete homes along Fallujah's urban fringe as he squinted into the setting desert sun. But his obscured view was enough to sense trouble.

A half-dozen houses were flattened. Others were punched with tank rounds. Each of them, Stevenson said, had been used by insurgents to fire at his bunker, which is fortified with dirt-filled mesh barriers.

Iraqi police officers and National Guardsmen, who should have been patrolling the streets, were nowhere to be found. A dusty pile of canvas 100 yards away provided the only reminder of the Fallujah Brigade, the now-disbanded Iraqi security force that was supposed to restore order here. The canvas had been one of the brigade's tents. It was gunned down after several members took potshots at Stevenson's men.

"Fallujah has become a cancer," declared Stevenson, echoing a metaphor used by several senior U.S. commanders in Iraq.

A collection of anti-American forces -- former Baath Party loyalists, Islamic extremists and foreign militants -- have been expanding their presence in Fallujah since the Marines withdrew from positions in the city in April and handed over responsibility for security to the Fallujah Brigade. According to U.S. military officials and residents, the insurgents have since taken over the local government, co-opted and cowed Iraqi security forces, and turned the area into a staging ground for terrorist attacks in Baghdad, located about 35 miles to the east.

But the U.S. military command in Iraq is in no hurry to order the Marines back into the city. Officers such as Stevenson, a tall Californian whose unit, the 2nd Battalion of the 1st Marine Regiment, would be among the front-line forces in an offensive, are biding their time in bunkers and observation posts outside Fallujah. Most of their days are spent keeping a highway around the city free of roadside bombs.

Instead of sending Marines charging into Fallujah as they did in April -- a move that radicalized residents and drew scores of fighters from outside Iraq to join the battle -- U.S. commanders say they want to wait until Iraq's new army is large enough, and trained enough, to assume a leading role in retaking the city.

"It doesn't do any good for us to go in and clean it up if it's a pure United States or coalition operation," said Lt. Gen. John F. Sattler of the 1st Marine Expeditionary Force, the top commander responsible for Fallujah and the rest of western Iraq. "We need Iraqi security forces with us. We need to be side by side when we move in, so that when it is said and done, when you open your door the next day and look out, there's an Iraqi policeman, an Iraqi National Guardsman, an Iraqi soldier on your street."

Sattler's predecessor, Lt. Gen. James T. Conway, who relinquished his command earlier this month, insisted that "the Marines we have there now could crush the city and be done with business in four days."

"But that's not what we're going to do," Conway said. Since the handover of sovereignty to an interim Iraqi government in late June, he added, Fallujah "is an Iraqi problem. If there is an attack on the anti-Iraqi forces that inhabit the city, it will be done almost exclusively by Iraqis."

If Iraqi forces take the lead in an offensive, the commanders said they hope that many residents would opt not to fight. That strategy could also deprive insurgent leaders of one of their most potent recruiting messages: that Fallujah needs to be defended against an onslaught of American forces. One Marine officer said the U.S. goal was "to split the city, to get the good people of the city on one side and the terrorists on the other."

Marine officials said they hoped to follow the strategy employed in Najaf last month, when a combination of U.S. and Iraqi forces pressured militiamen loyal to a rebel Shiite cleric, Moqtada Sadr, to vacate a religious shrine. Sadr eventually agreed to a peace deal that called for U.S. troops to withdraw from the city and for newly minted Iraqi army troops to patrol the area. U.S. Marine commanders expressed optimism that a joint U.S.-Iraqi force, employing Iraqi units from outside the city, might eventually succeed in pacifying Fallujah. When Marines withdrew from the city after a three-week offensive in April, they relied on the Fallujah Brigade, made up of local members of the old Iraqi army, to restore order. Instead, the unit melted into the insurgency.

In an interview earlier this month, Conway said he did not believe that the assault on Fallujah, which he said he was ordered to carry out in April after four American security contractors were murdered and mutilated there, was the best course of action. Instead, Conway said he favored targeted operations against insurgents 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. The offensive, he added, 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," he said.

Iraqi Troops Lacking

A U.N. Security Council resolution gives the U.S. military the freedom to conduct military operations as it sees fit in Iraq. But American commanders and diplomats in Baghdad have said they would not mount a major operation in Fallujah without the consent of Iraq's interim government. Senior Iraqi officials said it was highly unlikely that they would endorse military action that did not include a large contingent of Iraqi forces.

But it could take until the end of the year for enough Iraqi forces to be trained and equipped for a full-scale assault on Fallujah. There are only six Iraqi army battalions in service, each with about 700 soldiers, three of which are deployed in Najaf. Six more battalions are supposed to be trained by the end of October. By the end of January, U.S. officials hope to have 27 trained and deployed Iraqi battalions.

A senior U.S. military commander in Baghdad said there would not be enough Iraqi troops available between now and the end of October. "We're in kind of a window of vulnerability . . . because we don't have the capacity to do the things we know we need to do," he said.

The senior commander, who spoke on condition of anonymity, said Fallujah and the city of Samarra, an enclave 65 miles north of Baghdad where U.S. forces have avoided a decisive battle with insurgents, did not have to be pacified before national elections could be held in January. More important to quell, he said, were insurgencies in provincial capitals, such as Baqubah, about 35 miles northeast of the capital, and Ramadi, 60 miles to the west of Baghdad.

"Candidly, Fallujah and Samarra don't necessarily make the list," the senior commander said. "They're not provincial capitals. They're not major cultural centers."

While the U.S. military intends to intensify a joint campaign with Iraqi forces to attack insurgents by the end of the year, the effort likely will initially focus on small cities, the commander said. "Do you go right to Fallujah?" he said. "It's a big chunk to bite off. Can you isolate it and let it fester for a while?"

Some Marine officers in Fallujah contend that waiting for Iraqi forces to get trained will give the insurgents time to recruit new members, harden their defenses and plot new attacks. Among the insurgent ringleaders believed to be in or near Fallujah is Abu Musab Zarqawi, the Jordanian-born organizer of a string of car bombings, kidnappings and other attacks on U.S. and Iraqi security forces. He is one of the U.S. military's most-wanted men in Iraq.

"We need to take out that rat's nest," said one senior Marine officer in Fallujah, who spoke on condition of anonymity because his views contradict those of his commanders. "The longer we wait, the stronger they get."

That view is shared by a small cadre of Fallujah residents eager to end the hostilities and open the city to U.S.-funded reconstruction projects. "If they invade Fallujah now, it will be better," said Khamis Hassnawi, the city's senior tribal leader. "Every day that passes, the resistance increases. Their numbers increase. Their power increases."

Although the main road from Fallujah to Baghdad is blocked off by Marines, every other route into the city is open, allowing insurgents free passage to other parts of western Iraq and Baghdad. On most days, there are no checkpoints to search cars leaving Fallujah, where U.S. intelligence officials believe many car bombs are assembled.

U.S. military officers said that placing the city in a vise could lead Zarqawi's followers and other foreign fighters to flee to other parts of Iraq, making it harder to track their movements. The officers said that in the current situation, with insurgents remaining in the city, the military could rely on informants, reconnaissance drones and spy satellites to target them with airstrikes, which have occurred with increasing frequency.

"Zarqawi has massed his folks there and he is presenting targets for us on a regular basis," the senior military official in Baghdad said. "It's a heck of a lot easier to target the Zarqawi network when we see groups of 15 or 20 having a meeting in Fallujah than it is when we see three- to four-man cells spread out all over Iraq."

Conflicting Casualty Counts

Col. John Coleman, the chief of staff for the 1st Marine Expeditionary Force, estimated that hundreds of insurgents had been killed in airstrikes over the past several weeks in Fallujah.

Since Thursday, U.S. forces have conducted four airstrikes on what have been described as targets associated with Zarqawi's network in and around the city. Among them was a housing compound in an agricultural area about 15 miles south of Fallujah where the U.S. military said as many as 90 foreign fighters were meeting. The military said the strike, which occurred on Thursday evening, killed about 60 foreign fighters.

Witnesses and hospital officials disputed the account, saying that about 30 men were killed, many of them Iraqi. They said 15 children and 11 women also died in the attack.

Neither version of the strike could be independently verified.

The following night, the U.S. military said in a statement that it conducted "another successful precision strike" on a meeting of "approximately 10 Zarqawi terrorists" in central Fallujah. "There was no indication that any innocent civilians were in the immediate vicinity of the meeting location," the military said in the statement.

Neighbors interviewed by an Iraqi journalist working for The Washington Post described a different outcome. They said six people were killed: two foreign fighters meeting in the targeted house and a family of four -- a father, mother and two children -- living next door.

"The civilians are caught in the middle," said Rihab Aloosi, the director of the Fallujah Women's Center. "The U.S. forces don't give mercy to anyone and the holy warriors don't respect the houses and the families inside."

Competing Agendas

U.S. commanders say they believe the near-daily targeting of foreign fighters is starting to create fissures among insurgents in Fallujah. Initially, the outsiders were welcomed by the Mujaheddin Shura Council, an 18-member group of clerics, tribal sheiks and former Baath Party members who effectively run the city and elements of the insurgency. But now, many Fallujah residents appear to be growing weary of Zarqawi's followers, according to residents interviewed by telephone.

Zarqawi's agenda appears to extend well beyond the goal of residents, who want to keep U.S. forces out of the city. He and his supporters have turned the city into a base for wider attacks, particularly against Iraqi officials and security forces. His loyalists, many of whom adhere to the strict Salafi school of Islam, also have attempted to instill hard-line social restrictions, demanding that women cover their hair and hectoring men for not growing beards. Although Fallujah is a deeply religious city, many residents follow mystical Sufi beliefs, such as praying by the graves of relatives, which Salafis regard as blasphemous.

In what may be the strongest sign of tension between residents and foreigners, the head of the Shura Council, Abdullah Janabi, who had invited foreigners to the city in April, issued a statement on Friday calling Zarqawi a "criminal."

"We don't need Zarqawi to defend our city," said Janabi, who sought to draw a distinction between what he called "Iraqi resistance fighters" and foreign fighters engaged in a campaign against Iraq's infrastructure, foreign civilians and Iraqi security forces. "The Iraqi resistance is something and the terrorism is something else. We don't kidnap journalists and we don't sabotage the oil pipelines and the electric power stations. We don't kill innocent Iraqis. We resist the occupation."

Zarqawi's actions, Janabi said, have "harmed the resistance and made it lose the support of people."

Residents have reported skirmishes between residents and foreign fighters in recent weeks. The fighting has broken out after residents, fearful of airstrikes, have sought to evict foreigners from their neighborhoods, the residents said.

A delegation from the Shura Council intends to travel to Baghdad this week for discussions with Iraqi government officials aimed at a negotiated settlement that would allow Iraqi security forces to enter the city, council members said. But two demands of the council -- that non-Iraqi fighters loyal to the council be allowed to stay in Fallujah and that U.S. forces remain outside the city -- could scuttle the talks. Iraqi government officials have expressed an unwillingness to permit foreign fighters or create exclusion zones for U.S. forces.

Marine commanders remain skeptical that negotiations will bring peace to the city. "In the end," Conway said, "there will be a fight in and around Fallujah."

Washington Post special correspondents in Baghdad and Fallujah contributed to this report.

A masked insurgent patrols in Fallujah, which has been under the control of militants since U.S. Marines withdrew from the city in April.Residents examine the destruction from a U.S. airstrike Friday in Fallujah. At least three people died in the attack.