The combination of wretched weather, long and insecure supply lines, and an enemy that has refused to be supine in the face of American combat power has led to a broad reassessment by some top generals of US military expectations and timelines. Some of them see even the potential threat of drawn-out fight that sucks in more US forces. Both on the battlefield in Iraq and in Pentagon conference rooms, military commanders were talking Wednesday about a longer, harder war than had been expected just a week ago, the officials said.

“Tell me how this ends,” one senior officer said Wednesday.

While some top planners favor continuing to press north, most army commanders believe that the pause in army ground operations that began Wednesday is critical. A relatively small force is stretched thin over 300 miles, and much of the army’s killing power, in more than 100 AH-64 Apache attack helicopters, has been grounded by persistently foul weather or by battle damage from an unsuccessful pre-dawn raid on Monday. To the east, the Marine Corps advance on the city of Kut was also hampered by skirmishing along its supply line and fuel shortages at the front.

More forces are coming, including the army’s 4th Infantry Division, which has begun pushing equipment from 35 ships into Kuwait after Turkey refused to allow a second front into northern Iraq. But it will probably take the better part of a month for that tank-heavy division to get into position and provide combat power. Other forces heading to this region, including the 3rd Armored Cavalry Regiment, at Fort Carson, Colo., and the 1st Cavalry Division, at Fort Hood, Texas, will require months to move their tanks and other armor from their bases into combat, the defense officials said.

Pentagon spokesmen rejected that pessimistic assessment Wednesday and insisted that the war is still going according to plan. “The plan has moved almost exactly with expectations,” Army Maj. Gen. Stanley McChrystal said at the briefing. “Fast where we expected it to be fast, gathering strength where we expected to do that. So the answer is, it’s right on the mark.”

But Secretary of State Colin Powell, a former chairman of the Joint Chiefs of Staff who maintains close ties to some senior army generals, seemed to break with part of that assessment, saying in an interview with National Public Radio broadcast Wednesday that it is becoming evident that the war “may take a little bit longer, don’t know how long.” He added that, “The point is we have had a good battle plan, and it’s a battle plan that will succeed.” In the short term, the army plans to secure its strained supply lines with a portion of the 82nd Airborne Division, now positioned near Kuwait City, and troops from the 101st Airborne Division, which is gathering at a forward operating base deep inside Iraq, army sources said.

The degree to which the supply lines have been stretched can be seen in the fact that the Third Division this week was alarmingly low on water and was also in danger of running short of food, the sources said. Heroic efforts have been made by truck companies and other logisticians, but a certain amount of chaos has developed, exacerbated by sniping and immense traffic backlogs from the Kuwaiti border. That traffic jam also has undermined Bush administration plans to quickly follow the US military advance with tons of food and other humanitarian relief to win support among Iraqis. “There’s tremendous fog out there,” an officer said, referring to the confusion of wartime operations, with logistical commanders struggling to figure out where various supply items are in a system that at times resembles “just a bunch of guys out there driving around.”

Commanders would like to have a 10-day supply of food, water, ammunition, fuel and other basic supplies before launching a concerted offensive, but equally critical are items such as batteries and vehicle parts.

Also, army commanders have differing views about how vigorously the war must be prosecuted in Iraqi cities and towns. “How bad do you want to do it? We have the capability to surround a city, cut off the water, cut off the electricity. We don’t want to do that,” said one general. “It’s all about having military success, not about attacking the civilian population. But you have to break his will, to make him understand that he will not win.”

But another officer noted that rooting out militiamen and other irregulars fighting in southern Iraqi cities would enormously complicate the US military effort, requiring more troops and far more supplies. “Let’s say you throttle Al-Najaf,” he said. “Then you’ve got 600,000 people in the city and surrounding region you’re responsible for providing food, water and medical care.” Each additional combat unit sent to Iraq also will add to the logistical strain, he said. Overhanging all developments in the war this week is the unsettling realization that thousands of Iraqis are willing to fight vigorously. During planning for the invasion of Iraq, worst-case scenarios sometimes predicated stiff resistance, but “no one took that very seriously,” an officer said.

“The whole linchpin of this operation was the reaction of the Iraqi people and the Iraqi ground force,” said retired army Col. Robert Killebrew, a specialist in war planning. “If they don’t turn, and so far they haven’t, we have a very different strategic problem facing us than when we went in.”

When army combat operations resume, major adjustments are likely in strategic goals and targets. The sources said that some of the major assumptions underpinning the US approach to Iraq are being discarded. The planned blitzkrieg to Baghdad has stalled. Airpower has delivered less than expected, and Saddam Hussein and those around him still appear to have a firm grip on the Iraqi military and people. In an extremely unusual battlefield action, two Army M1 Abrams tanks were badly damaged in combat Tuesday.

An army general and others said that rather than slice through Republican Guard defenders and drive straight for Baghdad, the army and Marines are likely to be forced to focus on wiping out most of the Guard divisions facing them south of Baghdad.

“I think you need to defeat them in detail,” said the general, using the military term for utterly destroying a unit. US military intelligence analysts believe that, in contrast to the heavily armored and well-equipped Medina, the Baghdad division has only 58 aging Soviet-era T-62 tanks. “I think you should ‘Pac Man’ the ring around Baghdad,” he said, referring to the 1980s computer game in which a big dot gobbled up smaller ones.

Retired Gen. Barry McCaffrey said the army and Marine forces converging on the Republican Guard south of Baghdad will have no choice but to continue to attack those Iraqi defenders. “We’ve got no option, we’re committed,” he said. But, he added, “I wouldn’t go into Baghdad before I had another armored division come up into my rear.” The question is whether the 3rd Infantry Division will be able to continue to fight the Republican Guard without reinforcements. “I think the Third ID is going to run out of steam pretty soon, both people and machines,” said Killebrew, the retired army planner.

But McCaffrey, who during the 1991 Gulf War commanded what is now called the 3rd Infantry Division, said he thought the unit was capable of taking on all three Iraqi Republican guard divisions in the so-called red zone that marks the capital’s defensive perimeter.