WASHINGTON (AP) _ Scores of U.S. cruise missiles and radar-evading bombers, leading waves of punishing NATO attacks, struck Serb air defenses, power grids, arms factories, airports, barracks and command and control centers across Yugoslavia and in Kosovo.

Two B-2 stealth bombers, each carrying 16 satellite-guided 1-ton bombs in the first combat test of the bat-winged plane, delivered some of the heaviest hits, including on command bunkers and air defenses, said a senior U.S. defense official who spoke on condition of anonymity.

The airstrikes, launched in darkness Wednesday about 8 p.m. in Yugoslavia (2 p.m. EST), were expected to continue tonight and possibly for weeks.

``It's going to take more than one day,'' Defense Secretary William Cohen said on NBC's ``Today'' show, citing Yugoslavia's ``fairly robust and redundant air defense systems.''

Cohen said NATO planners picked targets ``with great care.''

``We are attacking the military infrastructure'' that Serbian forces directed by Yugoslav President Slobodan Milosevic ``are using to repress and kill innocent people,'' Cohen said.

An official NATO bomb damage assessment will come from satellite photos and surveillance planes, Pentagon officials said. Camera footage from warplanes and pilots also will provide details.

The NATO attack began with sea- and air-launched cruise missiles, nearly 100, many aimed at the Serb's sophisticated air defense system, including up to 1,000 Russian-designed surface-to-air missiles with advanced guidance systems capable of shooting down allied planes.

U.S. B-52 bombers, F-16 fighter-bombers and F-117 stealth bombers, as well as Canadian F-18s and other NATO aircraft from 11 countries, also were among the 400-plane force.

U.S. and allied fighter-jets downed at least two Soviet-made MiGs. The Pentagon said no NATO aircraft were lost as Serbs engaged in dogfights rather than launch anti-aircraft missiles. One U.S. Air Force F-15 fighter jet did make an emergency landing today in Bosnia-Herzegovina, next door to Yugoslavia. But U.S. officials said it had been flying a routine mission over Bosnia when a hydraulic pump went awry, and was not damaged by Yugoslav air defenses.

Cohen refused to reveal what targets were hit, but a Navy official, speaking on condition of anonymity, said highly accurate Tomahawk missiles likely did severe damage.

At least one factory that makes parts for air defense systems was targeted, a U.S. official said, speaking on condition of anonymity.

Around Belgrade, NATO struck near a power plant and the Batajnica military airport, the main Serbian air base 10 miles west of the Serb capital. Four missiles also struck an aircraft plant at Pancevo, six miles north of Belgrade, destroying several small planes.

The central Serb town of Kragujevac, a major military-industrial center, was plunged into darkness after a heavy explosion, the private news agency Beta reported.

A power grid also was hit in the Kosovo capital of Pristina, and several heavy blasts came from around the nearby Slatina airport, as well, the official Tanjug news agency reported.

In neighboring Montenegro, which with Serbia forms Yugoslavia, an army military barracks in Danilovgrad burst into flames after being hit. One soldier was reported killed and three wounded. Serbian TV said several civilians were wounded in attacks throughout the country.

Lt. Gen. Nebojsa Pavkovic, commander of Yugoslav troops in Kosovo, said 40 targets were hit in the initial NATO waves, but he claimed that damage was ``minimal.''