BRCKO, Bosnia-Herzegovina (AP) _ Sgt. Corey Smith, U.S. Army, spreads the tar. Sgt. Richard Goodboe shovels the gravel. The 94th Engineer Battalion is filling yet another of the hundreds of potholes it has repaired on a 15-mile stretch of road in northern Bosnia.

The task is almost futile, as heavy vehicles used by the NATO-led peace force tear up the crumbling asphalt faster than crews can fix it.

But patching the crater-pocked road across the former front line is nothing compared to the challenge of trying to put this region back together.

The road the soldiers are working on links the city of Brcko, held by Bosnian Serbs, with territory held by the fledging Muslim-Croat Federation.

Serb territory and federation territory are supposed to be integrated into one Bosnian nation. Yet, hostility between the former warring sides is blocking cooperation _ especially around Brcko.

The strategic city on the Sava River border with Croatia was such a hot potato that its status was left unresolved by the Dayton peace accord, which ended 3 1/2 years of fighting in Bosnia. The Dec. 14 deadline for deciding Brcko's fate by arbitration looms.

Both sides say they need Brcko (pronounced BIRCH-ko): the federation because of the city's rail and river barge links to the world; the Serbs because it sits on a narrow strip of land connecting Serb territory to the east and west.

There is also bitterness. Muslims charge that Serbs killed up to 5,000 people in camps after overrunning Brcko in 1992. U.N. war crimes investigators have inspected one of 11 alleged mass graves in the area, but have not exhumed any.

Predominantly Muslim before the war, Brcko is now 99 percent Bosnian Serb. Many of its approximately 30,000 residents are Serbs who fled Sarajevo when the Muslim-Croat Federation assumed control of that city under the Dayton deal.

The Muslims who fled Brcko and its bombed-out suburbs want to go back.

``For 20 years I worked there and made a home for my family,'' said Mirzeta Redzepagic, 46, a high school teacher now in Tuzla. ``Of course, I will return to my home town. Everything that belonged to me is there. My life is there.''

Mirsad Dapo, Brcko's vice mayor in exile, says allowing the Bosnian Serbs to keep the town would legitimize the slaughter. ``The international community can redeem itself here by giving us back Brcko,'' he said.

Bosnian Serbs are just as adamant about keeping the town. They have ruled out any talks about Brcko itself, and want to push the border further south to widen their east-west corridor.

``Brcko is more important for us than peace,'' Bosnian Serb leader Momcilo Krajisnik said recently.

``It's them or us,'' said Miroslav Banjic, a Serb in Brcko. ``There will be a lot of blood if they try to return.''

Since December, Lt. Col. Anthony Cucolo, commander of the U.S. base camp just outside Brcko, has hosted weekly meetings of local leaders. Icy confrontation has given way to cordial networking.

But, ``quite honestly, I have not seen compromise,'' Cucolo said. ``There would have to be a change in the political leadership.''

Exiled deputy mayor Dapo said anything he is able to work out with Brcko's new leadership _ repairing a house or reopening the town's big meat processing plant _ get blocked by higher-ups in Pale, the Bosnian Serbs' political center.

Arbitration is going nowhere. The team is set _ a lawyer from each side, and U.S. envoy Roberts Owen _ but they have yet to meet. The Serb representative failed to show last week in Sarajevo, with no explanation.

Meanwhile, efforts are underway to rebuild the area's war-ravaged infrastructure.

Mines have been cleared from the Bosnian side of the Sava River, where fishermen whiled away a recent evening casting for catfish and carp. The forested Croatian bank is still heavily mined, Cucolo said.

NATO engineers have repaired a bridge over the river, although it is not yet open for civilian traffic. A blown up railway bridge is next on the list, financed by U.S. aid.

Maj. Terry Gamble, an Army reservist and professional railroad man overseeing the reconstruction, calls it a ``politically correct'' project: a federation design team, Croatian materials and Bosnian Serb labor.

But technical meetings sometimes degenerate into arguments over questions like who owns the equipment.

``Everything we do becomes entwined in politics,'' he said.

In the suburb of Brod, which saw heavy fighting, the United Nations is financing reconstruction of salvageable homes. New wooden frames for roofs sit atop a few red brick shells.

But no one has moved in yet, and the ``Earth Movers'' of Company B had the road pretty much to themselves as they worked amid the ruins.

``After we're gone,'' said Sgt. Thomas Hood of New York City, ``they'll have a better road to travel on _ if they so desire.''