WASHINGTON - If the Taliban lose power in Afghanistan, there is little guarantee that the country wouldn't once again face civil war, perhaps among ethnic groups and warlords who might harbor terrorists themselves.

The United States says a post-Taliban government must be broad-based, not protect terrorists and be acceptable to its neighbors, especially Pakistan, Iran and Russia. It wants to create a situation in which the Afghans can choose a government themselves.

The United Nations envoy to Afghanistan warns that achieving that would be difficult in a place with rampant poverty, mistrustful ethnic groups, decades of war and many weapons. "We cannot produce a solution out of a hat," said envoy Lakhdar Brahimi, who already quit the job once in frustration.

The immediate future remains unclear: The United States is bombing Taliban sites in an effort to defeat the ruling militia and end Osama bin Laden's terrorist network. But at least so far, the U.S. military has not bombed Taliban front lines near Kabul, which would help the rebel anti-Taliban northern alliance capture the capital.

That U.S. strategy led to criticism Thursday from the Washington-based envoy for the northern alliance, which calls itself the United Front.

"We don't see any merit in the delay," envoy Haron Amin said. "Our ground commanders are ready, and they want to make the move, and there's no coordination."

The Taliban and rebels, meanwhile, are fighting back and forth for a major city in the north. And no one knows if Taliban fighters are defecting in the pivotal southern areas, from where most Taliban support emanates.

"What Afghanistan might look like politically, economically, diplomatically after the military phase ... is very much a work in progress," said John Negroponte, the U.S. ambassador to the United Nations.

Among possible scenarios, should the Taliban be ousted:

_The United Nations could lead efforts to create a broad-based government, as the United States has suggested, perhaps a loose federation of tribes built around the 87-year-old former king, Zahir Shah. Turkey has offered peacekeeping troops. The northern rebels and Zahir Shah have agreed to a traditional Afghan assembly to choose leaders.

Brahimi cautioned against using peacekeepers, noting Afghanistan always has been hostile to foreign troops, even Muslim ones such as Turks.

In addition, some northern alliance factions have in the recent past profited from the country's drug trade and themselves harbored Islamic extremists who have launched terrorist raids into neighboring Uzbekistan, said Fred Starr, a Central Asia expert at Johns Hopkins University.

A recent U.N. report said most growing of opium poppies inside Afghanistan now is done in areas controlled by the northern alliance.

Settling on a new government will be difficult "because these are not great statesmen," Starr said. "These are warlords."

In addition, distrust between the northern groups and neighboring Pakistan is extremely high. Pakistan wants to ensure any new government would include ethnic Pashtuns from the south, now the backbone of the Taliban.

_The northern rebels might seize Kabul from the Taliban before an interim government could be installed, then refuse to give it up. The alliance comprises northern minority groups like Tajiks and Uzbeks, which means the southern Pashtuns probably would fight northern control of Kabul. That could create a new round of violence.

When northern alliance leaders were in power five years ago, bloody infighting among rival warlords killed tens of thousands of people.

_A de facto partitioning of Afghanistan. The likely arrangement would be for the northern alliance and other non-Pashtuns based in the north to gain support from Russia and Iran, and a Pashtun government based in the south to take support from Pakistan and moderate remnants of the Taliban.

"If the northern half of the country could be taken away from the Taliban, and some serious economic aid done there, we would have normalized the situation at least in a large area of the country," said Charles Fairbanks of Johns Hopkins, and could more easily prevent terrorism in the south.

Surrounding nations, fearing ethnic violence, probably would fight partition, however. There are groups of Pashtuns in the north, for example, who could become a focus of ethnic violence under partitioning.

Whatever scenario plays out, foreign aid will be key to bolster any legitimate governments. The United States walked away after financing the mujahedeen who fought against the Soviet Union, leaving the Afghans to deal with the poverty and chaos caused by 10 years of war against the Soviets and civil war thereafter.

Ridding Afghanistan of the Taliban, then leaving, would be the worst outcome, Fairbanks said.

"There's a particular problem with these stateless places like Afghanistan, Somalia, Yemen _ they produce a lot of problems, drugs, crime, terrorism," Fairbanks said. "It's essential to remain engaged in Afghanistan for a decade or so, to prevent terrorism all over again."

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On the Net: Library of Congress country study on Afghanistan: http://lcweb2.loc.gov/frd/cs/aftoc.html