ON HIS WAY to last week's NATO summit in Turkey, Defense Secretary Donald H. Rumsfeld made a scarcely noticed stop in a usually overlooked country: Moldova, a neighbor of Romania and Ukraine, and the poorest nation in Europe. Why bother? Officially the defense secretary made his visit to thank Moldova's government for the handful of troops it has contributed to the U.S.-led coalition in Iraq, and to encourage its continued participation in NATO's Partnership for Peace program. But implicitly there was more on his agenda, something that the Bush administration is right to pay attention to: Moldova's fragile and faltering independence from Russia.

A former Soviet republic, Moldova is one of several states that constitute an uneasy and unstable zone between the newly expanded borders of NATO and Russia. Even as it grows increasingly autocratic at home, the government of Vladimir Putin is seeking to reconstitute the Kremlin's power over these countries: It is using the leverage of its energy supplies and access to its markets but also more troubling tactics, such as support for separatist movements. In Moldova, Moscow backs a rebellious slice of territory the size of Maryland called Transdniestria, which is controlled by former Russian officials backed by Russian troops.

Five years ago Russia pledged at a summit of European and North American states to withdraw its troops from Moldova and another former republic, Georgia, by 2002. In 2002 it promised they would be removed by the end of last year. It broke both pledges and now is pressuring both those governments and the West to allow it to leave its soldiers in place indefinitely. In Moldova, the pretext for the continued deployment would be the safeguarding of a proposed settlement to the country's conflict that would give Transdniestria -- and thereby Russia -- a permanent veto over Moldova's foreign policy.

The Bush administration has been saying that Mr. Putin should meet his commitment to withdraw the troops; along with other NATO governments, it has held up ratification of a new agreement on the deployment of military forces in Europe until Russia complies. But the message has sometimes been mixed: The State Department has been generally supportive of "federalization" proposals for Moldova that the democratic opposition says would return the country to the status of a Russian satellite.

That's why Mr. Rumsfeld's visit was important: He stressed the commitment of the United States to "a reintegrated, sovereign Moldova" and said "it remains the position of all of those [NATO] countries that they will require that the Russians fulfill their obligations with respect to the removal of troops." That position ought to be a key element of the Bush administration's reaction to Mr. Putin's growing imperial ambitions.