The tiny village of Ushguli lies in an emerald-green valley in the far north of the republic of Georgia. Hemmed in by the snow-capped peaks of the Caucasus mountains, it's a jumble of slate buildings flanking a glacier-fed stream. When I last visited, local elders showed me around the medieval stone towers that dot the countryside. A millennium ago, defense was a self-help game, and families erected private fortresses to guard against vengeful neighbors and foreign raiders.

Political leaders in the United States and Europe are careening down a path that could make faraway Ushguli the eastern border of NATO. Foreign ministers from the transatlantic alliance's 26 member states will meet this week in Brussels to decide whether Georgia and Ukraine should take an important step toward membership. But Western leaders would be wise to act slowly, or the world's most successful military alliance could become as irrelevant as the ancient watchtowers of the upland Caucasus.

Last April, NATO put off both countries' applications but promised to revisit the issue in December. The August 2008 war between Georgia and Russia has sharpened the debate. To some Western observers, Russia's intervention in Georgia demonstrated the need to expand the alliance and block Moscow's imperial ambitions. Without the security guarantees provided by NATO membership, the logic goes, both Georgia and Ukraine will find themselves increasingly threatened by the bear lumbering forth from the Kremlin.

For leaders in Kiev and Tbilisi, the core advantage of membership is Article Five of the North Atlantic Treaty, the document that gave birth to the alliance in 1949. Under this provision, "an armed attack against one or more" allies in Europe or North America is considered an attack on them all. So far, the alliance has invoked Article Five only once: In the weeks following the terrorist attacks of Sept. 11, 2001, planes from more than a dozen nations provided security and intelligence assistance in the skies above the Eastern United States.

Neither Ukraine nor Georgia is slated to become a full member soon.

The issue at stake is whether they will be granted a "membership action plan," or MAP, setting out specific targets that Kiev and Tbilisi must meet before they can begin formal accession talks. The Bush administration is putting pressure on its NATO allies to push forward with the MAP. But in doing so, the United States is lowering the bar set for past applicants.

Countries that have joined the alliance since the end of communism — ex-Soviet satellites such as Poland and Romania and ex-Soviet republics such as Lithuania and Estonia — have been held to rigorous standards. Each has had to demonstrate that it can contribute security to the wider alliance, not just consume the security guarantee provided by Article Five. That approach has produced remarkable results: a historic peace treaty between Romania and Hungary, better minority-rights protections in the Baltic states, improved civilian control of the military in Poland.

But in the case of Ukraine and Georgia, NATO has fallen victim to grade inflation. In April, NATO leaders stated plainly that both countries "will become members of NATO," while leaving the precise timetable uncertain. Moving forward with the MAP now takes the alliance down a road with a predetermined endpoint — the extension of the "North Atlantic" to the eastern shores of the Black Sea and the peaks of the Caucasus.

Military alliances are the most serious international commitment societies can make. But politicians in Washington and Brussels have ignored their responsibility to justify the promise of blood and treasure they seem willing to make on their citizens' behalf. There are several things that more sober NATO members can do to decelerate the dash to the east.

First, NATO should demand real progress from Kiev and Tbilisi before instituting the MAP or any other form of enhanced relationship with the alliance. Georgia has used large-scale military force against its own citizens three times in the past 15 years. It has no nationwide independent broadcast media. It has never changed its head of state by holding a boringly ordinary election. Nearly a fifth of its territory is under the control of secessionist regimes.

Charles King is chairman of the faculty of Georgetown University's Edmund A. Walsh School of Foreign Service. His most recent book is "The Ghost of Freedom: A History of the Caucasus."