"I am convinced that the dangers of acting are far outweighed by the dangers of not acting," Clinton said in a speech from the Oval Office.

"By acting now, we are upholding our values, protecting our interests and advancing the cause of peace," added Clinton, who said failure to act would be seen as "a license to kill" helpless civilians in Kosovo.

He spoke as U.S.-led NATO forces blitzed one-ton bombs and cruise missiles on Serb military targets in Operation Allied Force and the $2 billion radar-evading Stealth B-2 bomber saw its first military combat.

Operation Allied Force's goal is to punish Serb strongman Slobodan Milosevic for his "brutal repression" of ethnic Albanians in Kosovo, to gut the Serb war machine - and show NATO is serious about fighting aggression, Clinton said.

NATO officials reported at least three dogfights involving American jets and Serb MiGs and said at least one MiG was shot down as wave on wave of NATO warplanes struck.

Defense Secretary William Cohen confirmed air-to-air combat but stressed: "Our aircraft have safely returned."

Serb TV claimed a NATO plane was shot down, but Pentagon officials denied any U.S. planes were shot down and NATO said no planes from other allied nations were lost either.

There were no immediate reports on the success of the airstrikes - U.S. Joint Chiefs chairman Hugh Shelton said "it's really too early to get into battle damage assessments."

Pentagon officials said the airstrikes could last for days or weeks - but Milosevic could end them by agreeing to the peace deal to restore autonomy to Kosovo and bring in 28,000 NATO peacekeepers including 4,000 Americans.

The airstrikes came after months of talks failed to convince Milosevic to end his crackdown on Kosovo, where 90 percent of the people are ethnic Albanians.

Some 2,000 have died over the past year as the Kosovars battled for freedom and Milosevic's troops burned villages.

Clinton last night came armed with a map to show Americans where Kosovo is and argue its importance, saying it's just 160 miles east of Italy - "less than the distance between Washington and New York."

He stressed the humanitarian goals of Operation Allied Force as he accused Milosevic of "genocide in the heart of Europe" and painted a grim picture of innocent civilians mowed down in cold blood by Serb troops.

The Kosovars are being "forced to kneel in the dirt and sprayed with bullets ... fathers and sons together lined up and shot," Clinton said.

The president said there is a risk to U.S. pilots and civilians on the ground and a risk that the Serbs will retaliate elsewhere against America or its allies - but warned that will prompt a "forceful response."

Clinton said he is ready to send U.S. peacekeepers to Kosovo if Milosevic agrees to the peace deal but repeated that there will be no ground war, only airstrikes - "I do not intend to put our troops in Kosovo to fight a war."

Air-raid sirens wailed across Belgrade and Kosovo's capital of Pristina, Serb TV showed dramatic footage of burning structures with flames shooting up into the night but claimed no military targets were hit in the first wave.

The day's military moves by NATO prompted angry threats from Russian President Boris Yeltsin to take military action to counter the offensive which he described as "nothing more than open aggression" against the Serbs, Russia's historic ally.

An outraged Yeltsin pulled Russia out of its partnership with NATO, declaring Russia reserves the right to take "adequate measures, including of a military character, to ensure its own and general European security."

Clinton administration officials brushed off the risk of any Russian military action, saying the financially ailing nation has too many problems of its own.

The Kosovo operation brought the first combat use of the radar-evading B-2 Stealth bomber, the world's most advanced and expensive warplane.

Two of the bat-shaped planes successfully flew from their Missouri base to the Balkans, where each dropped 16 one-ton satellite-guided bombs on Serbian military targets, sources said.

The first wave was launched at 2 p.m. New York time and involved sea-to-land cruise missiles and more than three-dozen cruise missiles shot from six B-52 bombers from over the Adriatic Sea.

The B-52s took off from British bases yesterday morning, sparking the first reports that the military action was under way.

Witnesses reported bombs rocking Belgrade, Yugoslavia, near the Batajnica military airport and a power plant - as well as four major explosions that plunged Kosovo's capital city of Pristina into darkness.

-- Brian Blomquist - 3/25/99