NATO on Wednesday authorized the deployment of a force of 3,500 troops, which is to include Americans, to Macedonia.

Wednesday's authorization means the first troops will be arriving within 48 hours. The entire British-led force, dubbed Operation Essential Harvest, is expected to be in Macedonia within 10 days to two weeks.

The force, including several hundred U.S. troops focusing on limited logistical duties, is going to Macedonia to collect and destroy rebel arms and assist in ending animosity between Macedonians and ethnic Albanians. NATO has placed a 30-day time limit for the mission.

The rebels took up arms six months ago, claiming they wanted more rights for the ethnic Albanian minority. NATO moves in under a peace accord signed last week by the country's ethnic Albanian and Macedonian leaders.

On Tuesday, the North Atlantic Council — made up of ambassadors from NATO's 19 member nations — authorized Gen. Joseph Ralston, supreme allied commander in Europe, to launch the full mission. But they gave members until noon Wednesday to object.

None did, and when the deadline passed the authorization was automatic.

Macedonia's government welcomed NATO's decision on Wednesday and pledged its cooperation.

"We have big expectations from NATO's mission," said Stevo Pendarovski, an adviser to Macedonian President Boris Trajkovksi.

An ethnic Albanian rebel spokesman known as Besniku also cautiously welcomed the decision, "provided that NATO will be evenhanded with both sides."

"If not, we still have arms in our hands — and more importantly, we have the will of the Albanian people to go until the end in order to gain their rights," he said.

Ralston stressed that while nobody could promise the current cease-fire would hold, the risk of waiting was greater than the risk of moving quickly, diplomats and officials said.

Although violence has subsided since the cease-fire, an explosion early Tuesday rocked Sveti Atanasi Orthodox church in the town of Lesok, about five miles from Tetovo, Macedonia's second-largest city. Government officials blamed the rebels, who denied responsibility.

The Macedonian government claimed Wednesday that ethnic Albanian insurgents have an arsenal vastly greater than previously estimated, adding potential complications to NATO's arms-collection mission.

The Interior Ministry, which controls the police forces, said the rebels have 10 times more firepower than previously believed — about 85,000 weapons, not counting individual rounds of ammunition. The rebels say they have only 2,000 weapons.

"There's been no decision or agreement" on how many rebel arms will be collected, said Maj. Barry Johnson, a NATO spokesman. "The figure must be agreed by all sides involved."

The Bush administration has made no secret of its desire to disengage from the Balkans, although it has promised not to make any dramatic troop reductions without consulting with its European allies. U.S. troops in Macedonia will likely play a behind-the-scenes role, such as monitoring unmanned reconnaissance flights, rather than collecting weapons.

Roughly 9,000 Americans remain on patrol in Europe's most volatile region — 500 in Macedonia, 5,000 in Kosovo and 3,500 in Bosnia-Herzegovina.

Ralston and NATO Secretary-General Lord Robertson assured the council that all the alliance's preconditions for deployment have been met, one diplomat said, speaking on condition he not be identified.

The NATO mission will deploy troops to several locations. Headquarters will be near Skopje. One battalion will be northwest of Skopje and others will be at Petrovec Airport, Kumanovo and Krivolak.

Ralston, who is an American Air Force general, will carry out the deployment, to be led by Britain, with about 1,800 troops, and another 1,700 drawn from 10 other European nations and the United States.