WASHINGTON, April 26 — When American commanders on the outskirts of Najaf and Falluja peer into the two troubled Iraqi cities, they see very different problems. Each place has its own culture, each harbors a different enemy, and each offers its own potential allies to help calm a volatile situation.
Those differences help explain why the American military appears to be taking a softer line in Najaf than in Falluja, where the threat of an outright assault is never more than a day or two away.
Najaf is home to the Shrine of Ali, one of the most sacred pilgrimage sites for Shiite Muslims. Moktada al-Sadr, the leader of the rebellious Mahdi Army militia, remains entrenched there. But American military officials have stopped proclaiming that they will capture or kill him, despite the fact that his fighters continue to confront occupying forces there and in a slum of Baghdad.
Senior Pentagon and military officials said Monday that they had no intention of sending American forces into the center of Najaf, near the holy sites. Even though officials said Mr. Sadr's militia must immediately stop stockpiling weapons in shrines and mosques there, they seem to have accepted that any attack could inspire explosive demonstrations throughout the Shiite world.
That stance contrasts starkly to the one adopted by American commanders at Falluja, a bastion of Sunni support for Saddam Hussein west of Baghdad where marines are poised for an offensive against entrenched urban guerrillas should no political solution be reached. There, the marines on Monday blasted away the minaret of a mosque being used as a sniper nest by insurgents.
Brig. Gen. Mark P. Hertling, an assistant commander of the Army's First Armored Division, which has forces outside Najaf, said late Monday that senior officers had no intention of moving into the city center.
General Hertling said American troops had moved from Baghdad to bases near Najaf to bring a muscular military presence to the area and to guard the work of the civilian occupation authority there. "We have not and do not foresee conducting military operations within the holy city," he said in a telephone interview.
Pentagon officials, of course, say that no options can be ruled out should the situation in Najaf flare out of control at Mr. Sadr's bidding. But the strategy to isolate and marginalize the cleric is specifically designed to sap his strength.
"Sadr gains his power by confronting the United States," one senior Pentagon official said Monday. "We do not intend to let him grow in power. We will deny him the opportunity to confront us."
While American forces are isolating Mr. Sadr in Najaf, they are looking to mainstream Shiite clerics and political parties to marginalize him. These local leaders have their own reasons to eliminate Mr. Sadr as a rival for the majority Shiite vote in the new Iraqi government, although they must be careful not to appear to be working on behalf of the widely unpopular American occupation.
In contrast, senior Pentagon officials express little confidence that the community and business leaders acting as interlocutors in Falluja actually hold sway over the insurgents, or even a majority of that Sunni city's residents. That is why American commanders at Falluja have said they would soon begin sending patrols of marines and Iraqi forces into the dusty streets of the Sunni stronghold west of Baghdad, backing them up forcefully if need be.
The Shiite religious establishment in Najaf expresses no affection for Mr. Sadr, partly because of his father's split with the other grand ayatollahs and partly because of Mr. Sadr's alleged involvement in the killing last April of Abdul Majid al-Khoei, a respected American-backed cleric who was returning from exile.
American officials announced early this month that an Iraqi judge had issued a warrant for Mr. Sadr's arrest in the killing. Since then, some leaders in Najaf have been more open in criticizing Mr. Sadr, perhaps emboldening Mr. Bremer to call for residents to act.
An aide for one grand ayatollah in Najaf said in an interview that the marjaiah, a group of four powerful clerics, wanted Mr. Sadr to leave town but would also condemn the Americans if they invaded Najaf.
On Friday, an imam in the Shrine of Ali, Sadr al-Din al-Kubanchi, told 2,500 worshipers that armed men taking refuge in Najaf or using holy sites as a shield were cowards.
A group calling itself "Najaf's Intellectuals" handed out fliers two weeks ago about the killing of Mr. Khoei. The letter listed the names of 24 people tied to Mr. Sadr who it said took part in the mutilation of Mr. Khoei outside the golden-domed Shrine of Ali. The letter said that Mr. Khoei ran to Mr. Sadr's office to seek refuge, only to have Mr. Sadr close the door in his face and leave him to the mob. Other reports from Najaf indicate that residents may actually be attacking members of Sadr's militia, but there was no independent confirmation.
There is another difference between the two cities. While the fighters in Falluja are mounting credible small-unit military missions, and have the support of at least some percentage of the population, Sadr's militia in Najaf are mostly young, unemployed men with little military experience, and their insurrection is said by American commanders to have raised the ire of local shopkeepers and merchants.
Hundreds of members of the undisciplined Mahdi Army control the downtown, blocking main roads and guarding the Shrine of Ali, as well as much of the nearby town of Kufa.
American and allied officials say that attacking Mr. Sadr's militia in Najaf could stir them up elsewhere. He has a strong base of support in Sadr City, a slum of two million people in northeastern Baghdad.
In Basra, though, where suicide bombers killed more than 50 people last week, the allied commander in southern Iraq said that Mr. Sadr is not personally popular but that his words strike a populist chord.
The commander, Maj. Gen. Andrew Stewart of the British Army, said moderate Shiite clerics had warned him that their tacit support of the occupation would end, and end violently, if American-led forces attacked Najaf. "Shias have told us that shrine must be untouched," he said. "If it's destroyed or damaged, that would be seen as an attack on the Shia as a whole."
Edward Wong contributed reporting from Baghdad for this article.