KIRKUK, Iraq - He has never set foot in the State Department, but 30-year-old Capt. Eric Baus, of Collingswood, N.J., was the man conducting diplomacy for the United States in this strategically important northern city yesterday.

Baus, a company commander in the Army's 173d Airborne Brigade, began the day with what seemed a fairly straightforward mission: clear and occupy a compound that had been the center of municipal government under Saddam Hussein.

After hours of negotiating with Kurdish officials and militiamen occupying the center, Baus and his paratroopers had learned a lesson about what U.S. forces face as they seek to restore order while keeping a lid on volatile ethnic tensions: Nation-building makes winning a war look easy.

"This is just a power struggle, and we can't get in the middle of it," Baus said at one point, as he tried to figure out the difference between Kurdish police, who will be allowed to carry guns in Kirkuk, and Kurdish soldiers, who are supposed to be barred from the city altogether.

Baus' day started simply enough.

After he got his orders, he set out in his humvee with about 40 infantry soldiers following on a rented flatbed. Crowds of Kurds cheered and waved, as they have for every American vehicle they see.

Baus was counting on having to evict a few Kurdish soldiers, whom he knew had already ransacked the place. But when he arrived - without an interpreter - he found the enormous complex filled with scores of Kurds in various uniforms, most of them toting AK-47 assault rifles. Outside, a crowd was assembled for what looked like a political rally.

No one had bothered to tell Baus that Jalal Talabani, head of the Patriotic Union of Kurdistan, the faction that holds sway in Kirkuk, had scheduled an appearance in the building that Baus was intending to take.

"I think right now, discretion is the order of the day," he said after counting about three Kurdish guns for every American one. He called for his boss, Lt. Col. Dominic Caraccilo, the battalion commander.

His soldiers stood around, bristling with machine guns and grenades. As Baus waited, he spoke with Mahmoud Mahmoud, a U.S.-educated civil-engineering professor.

"Right now, we need the Americans to keep the peace," Mahmoud said. "There are many [Kurds] carrying weapons, and they say, 'Show me your card or we kill you.' If the Americans capture the buildings held by the PUK and the KDP [Kurdistan Democratic Party], the people will feel better."

Baus heartily agreed. He had spent his first weeks in territory controlled by the KDP, and now he was in PUK-land. His goal was to stay neutral and be seen as an independent force looking out for all the civilians in Kirkuk, a city that includes Kurds, Arabs and Turkmen.

When Caraccilo arrived and the paratroopers asked to speak with the man in charge, they were taken to the office of Faridon Abdulkadir, who described himself as the PUK's interior minister.

After asking his advice about which sites in Kirkuk the 173d should occupy as a show of force, Caraccilo and Baus spent several minutes requesting that Abdulkadir clear all the soldiers out of the building.

"What about my guys?" Abdulkadir asked, referring to his team of bodyguards.

"I don't understand why you need guards with machine guns," Baus said. "If you stay here, we will protect you. If you have civilian staff, that's fine."

He added: "Whether it's official or unofficial, this can't turn into a PUK political office."

Baus also explained that the paratroopers intended to make Kirkuk a weapons-free zone and would seize any guns they see. They have set up checkpoints to accomplish that - even as they acknowledge they will never be completely successful.

Lengthy discussion followed over whether PUK-sponsored traffic police could patrol the city and man checkpoints in blue uniforms. Eventually, Baus assented, satisfied that they would not look like soldiers. He wondered, though, whether the PUK's militiamen would just switch to blue uniforms.

When it was over, Caraccilo rolled his eyes. "We're going to decide who we're going to put in the regime in Baghdad next, too," he said wryly.

The Kurdish soldiers left peaceably. Some even tidied up the compound for the Americans. Abdulkadir was allowed to remain.

For the moment, the well-armed Kurds seemed willing to follow American orders.