WHAT DOES it take for outside powers to rebuild a war-ruined and badly divided country? Bosnia offers a state-of-the-art -- and sobering -- example. Seven years after a U.S. intervention helped end its civil war and Western troops poured in to keep the peace, the Balkan nation of 3.5 million remains far from able to live on its own. The good news is that the horrific fighting that killed a quarter of a million people in less than four years has not been renewed, that several hundred thousand refugees and victims of ethnic cleansing have returned to their homes, and that peaceful and free democratic elections were held this month for all levels of government -- the sixth elections to be staged in as many years. But the peace continues to depend on 12,000 foreign troops, including 2,000 Americans; the functioning of government relies in no small part on the interventions of a Western "high representative" with near-dictatorial powers; and, most discouraging of all, the victors in the recent elections were the same nationalist parties that tore the country apart a decade ago. Bosnia is not now a failed state, but it is a center for the trafficking of women and narcotics, a hide-out for war criminals and a steady drain on Western aid and defense budgets. It's not likely to collapse soon, but neither will foreign troops and administrators likely be able to safely pull out for many years to come.

The Bush administration has from its onset disparaged the nation-building projects supported by President Clinton in Bosnia and elsewhere in the Balkans, and it has occasionally threatened to withdraw American troops. In Afghanistan the administration has deliberately pursued a different model, eschewing international administration or a large foreign peacekeeping force and trying to invest a skeletal Afghan government with authority. But that strategy has left Afghanistan at the mercy of brutal warlords and at perpetual risk of chaos. So now White House officials, looking forward to Iraq, are floating still another model: direct administration by the U.S. military. The idea is a regime that would last for a period of several years while a civilian democracy was constructed.

The Bosnia experience offers some support for this more muscular postwar scheme. Paddy Ashdown, the veteran British politician and statesman who is now the high representative in Bosnia, has pointed out that the repeated elections in that country have sometimes impeded rather than advanced the progress of desperately needed economic and political reforms. Most of the important changes in the country, from guarantees for returning refugees to the purging of criminals from government, have happened on the orders of Mr. Ashdown and his predecessors. And further progress is unlikely unless Western governments tightly condition continued aid on concrete steps by the Bosnians. In short, while democracy should be a central aim of postwar nation-building, it cannot necessarily be the starting point -- and even if it is, a strong outside authority is essential.

Yet Bosnia also shows that it is far easier to take over a devastated state than to let go of it. The Clinton administration originally promised, with calculated insincerity, that U.S. troops would be needed only a year. They have now been there nearly seven, and Mr. Ashdown and other international experts believe they will be needed for several more years at least. Iraq offers a far larger and more complicated challenge of nation-building; it can only be expected that any postwar mission will be even harder and take still longer. The Bush administration needs to be honest, both with itself and with the public, about the scale of the coming commitment -- and scrupulous about planning for the long term. Just as it unwillingly inherited the Clinton administration's scheme for Bosnia, its successors will surely be burdened with implementing the decisions made in the coming months about Iraq.