Correction Appended

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A second Western diplomat who also follows Afghanistan said: ''These ideas of trying to create government, institutions, policies out of nothing -- they can't be done. There's going to be a messy give and take.''

For now, with few resources to exploit in the south, American planners are concentrating on the north, and particularly Mazar-i-Sharif. If it falls, the administration will have a tangible victory in hand that might allay concerns in Europe and elsewhere about the bombing strategy.

But the Northern Alliance remains a largely untested force, and the difficulties of marshaling it, or any faction, were clear enough at the Pentagon today. ''There is not one 'the' Northern Alliance,'' the Pentagon spokeswoman, Victoria Clarke, said. ''There are different factions. And there are tribes in the south. And there are people within the Taliban itself that oppose the Taliban regime.''

To see what she meant, consider the resistance forces in the north who, with the support of American bombing and American advisers, are pressing to attack Mazar-i-Sharif.

The city, which lies along the Silk Road through Central Asia, is widely seen as the battleground where the control of northern Afghanistan will be decided. As Mazar goes, Northern Alliance leaders say, so goes the rest of the north.

The city sits on a highway that touches many of the main pockets of anti-Taliban activity, from Herat in the west to Taliqan in the east. It also controls a highway that runs from Kabul to Uzbekistan. Its capture by the Northern Alliance could open up the area to greatly increased assistance from the United States, which has established an important base in Uzbekistan.

The campaign for Mazar-I-Sharif brings together two colorful Northern Alliance commanders: Ostad Atta Muhammad, who was a mujahedeen commander at age 18, and Rashid Dostum, an Uzbek warlord long known for his healthy appetites and fickle loyalties. Until recently, they were making little progress, gaining ground one day and losing it another.

According to an aide to General Muhammad, who is in charge of the Mazar campaign, that began to change when Americans on the ground pinpointed Taliban positions for the bombers, helped plan the ground attack and gave orders to commanders and soldiers alike.

The Americans, who apparently wear no uniforms, are said to have set up a camp in Dara-i-Suf, a remote village in the mountains south of Mazar-i-Sharif.

But along the 50-mile front that stretches from the Tajik border to the outskirts of Taliqan, the military campaign seems uneven. For two weeks, American B-52's and fighter-bombers have been pounding Taliban positions along a five-mile area just south of the border with Tajikistan. The Taliban positions sit dangerously close to an important supply route for the Northern Alliance.

The commander of rebel forces there, Mamoor Hassan, says his units are ready to attack, and at the same time he complains that his food and ammunition will last only four days.

In that way he differs little from his comrades in the Northern Alliance. American helicopters have been spotted in the air along Afghanistan's northern borders, but the presence of American advisers here and nearer to Kabul has been kept quiet.

The Weapons

Change in Air Forces May Be in Works

For the Pentagon, every war becomes a laboratory for new weapons and tactics. In the Persian Gulf war, the military sent the Joint Stars aircraft, a surveillance plane that tracks troop movements on the ground, while it was still in development. The plane helped track armored columns of Iraqi Republican Guard.

In this campaign, a high-flying, long-range drone called Global Hawk has been pulled out of development and sent to the front, to expand the military's reconnaissance abilities.

The air campaign, now entering its fifth week, has seen a role reversal in combat flights. Unlike the case in the gulf war, in which Air Force warplanes dominated the skies, the lion's share of the bombing missions in this war have been flown by Navy F-14's and FA-18's off carriers in the Arabian Sea.

That may change soon. The Pentagon is assessing airfields in Tajikistan and other Central Asian countries that would allow Air Force fighters now flying long missions from the Middle East to operate from bases much closer to Afghanistan.

Not all the American technology has worked perfectly; it never does. Errant American bombs have strayed into residential neighborhoods, reportedly owing to malfunctions or human target-selection mistakes. Many Afghan civilians have been killed.

B-52's and FA-18's mistakenly attacked warehouses used by the Red Cross for relief supplies when military officials forgot to take the buildings in Kabul, the Afghan capital, off a target list.

Although the American military is famous for its high-technology precision weapons, the Pentagon has relied on some of its oldest arms to attack Taliban ground forces and try to shatter their will to fight.

B-52 bombers, upgraded since the Vietnam War, are dropping dozens of 500-pound unguided bombs on Taliban troops dug in along the front lines. Lumbering AC-130 Spectre gunships rain heavy caliber machine-gun and cannon fire down on enemy positions as they did in Southeast Asia more than three decades ago.