Armed Yugoslav troops seized control of the main airport in Montenegro today, raising tensions between federal authorities loyal to President Slobodan Milosevic and the independence-minded republic.

The move took place one day before Montenegro planned to take full control over the strategic facility, which serves as both the republic's main commercial airport and a Yugoslav air force base.

Military trucks rolled onto the main runway at Podgorica Airport about 5 p.m., and Montenegrin Deputy Information Minister Abaz Dzafic said troops loyal to Milosevic had taken over the control tower, banning all flights.

Troops were also seen along roads leading to the airport, located about 10 miles from the Montenegrin capital, Podgorica. Paramilitary police loyal to Montenegrin President Milo Djukanovic remained in the main airport building.

Frustrated by Milosevic's autocratic policies, Montenegro's leadership has recently made a series of steps to split from Serbia, the larger republic in the Yugoslav federation. This has angered Milosevic's regime, raising fears of a possible military crackdown against Montenegro.

The Belgrade government made no statement about the move on the airport. Tonight, however, the independent Belgrade television station Studio B reported that the "misunderstanding" between the Montenegrins and the army had been resolved and the airport would reopen Thursday.

But a Montenegrin source at the airport, reached by telephone from Belgrade, said the standoff was continuing and denied knowledge of any agreement.

The airport's civilian director, Drago Milanovic, said Yugoslav authorities cited "security reasons" in taking over the facility. Milanovic said federal authorities refused to allow Montenegrin Airlines' regular Belgrade-to-Podgorica flight to leave tonight.

The Montenegrin government has opposed Milosevic's confrontational policies, including the crackdown on ethnic Albanians in the Serbian province of Kosovo that provoked the 78-day NATO bombing campaign this spring.

In Washington, spokesmen for the White House and Pentagon said U.S. officials were watching the situation closely but no NATO military action was imminent. An aide to Gen. Wesley K. Clark, NATO's top military commander, noted that the general had months ago requested and received permission to prepare contingency plans for just such a Serbian move, as well as other possible threatening actions by Milosevic. But the aide added that U.S. and European authorities were trying to get a more detailed picture of the Yugoslav action and its significance.

Staff writer Bradley Graham in Washington contributed to this report.