BELGRADE, Yugoslavia (AP) -With NATO missiles striking Belgrade night and day, the first batch of Apache attack helicopters touched down in Albania yesterday as the Western allies intensified their air campaign against Yugoslavia.

The arrival of the long-awaited U.S. anti-tank helicopters represents a significant boost in NATO's capability to destroy tanks and troops of Yugoslav forces blamed for atrocities against Kosovo Albanian civilians. It wasn't known when the helicopters would go into action.

NATO spokesman Jamie Shea said the alliance, bolstered by extra aircraft, is hitting double the number of targets it struck during the first two weeks of the campaign, now entering its fifth week.

Early yesterday, NATO missiles slammed into a high-rise building which includes offices of President Slobodan Milosevic's ruling Socialist Party and eight broadcast stations, one of them owned by Milosevic's daughter. A senior Yugoslav official called the strikes part of a "genocidal flying circus" perpetrated by NATO.

Hours later, NATO launched a rare daytime strike in the capital area, severely damaging a railway bridge over the Sava River a few miles west of Belgrade.

The state news agency Tanjug said the missiles hit a compound near the Kosovo town of Djakovica containing Serb refugees from fighting this decade in Bosnia and Croatia, killing at least 10 people and injuring 16. There was no way to independently verify the report.

The strikes near Belgrade and the arrival of the Apache helicopters signaled the North Atlantic Treaty Organization's resolve to escalate the conflict until Milosevic accepts a Western-dictated peace plan for Kosovo, a province of Yugoslavia's republic Serbia with an overwhelmingly Albanian population.

Apaches are among the most lethal tank-killers in the NATO arsenal, each armed with 16 Hellfire missiles, 70 mm rockets and a 30 mm cannon that fires 625 rounds per minute.

Their use in combat would also mark the U.S. Army's entry into a conflict which has been waged by the Air Force and Navy.

"There's of course risk to us," Army Capt. Mark Arden of Washington, D.C., said in the Albanian capital, Tirana. "But the risks to the Serbs, I would say, are great."

The Apaches are expected to be used initially against Serb targets in southwestern Kosovo. Ethnic Albanian rebels fighting for an independent Kosovo have regrouped there after Serbs drove them from many of their traditional strongholds.

International monitors said 18 rebels were wounded and two killed in a second straight day of heavy fighting yesterday in southwestern Kosovo near the Albanian border.

As the air campaign escalated, alliance spokesmen said NATO blasted more than 20 targets early yesterday.

Besides the bridge outside Belgrade, two others over the commercially important Danube River also were wrecked around Novi Sad, Serbia's second-largest city. NATO said it is targeting the bridges to prevent the army from resupplying its forces in Kosovo.

Yugoslav officials expressed outrage at the pre-dawn strike on the 23-story Socialist Party building in Belgrade, calling it a purely civilian target.

"This genocidal, flying circus of the NATO alliance has caused huge destruction," said Goran Matic, a federal government minister. "But citizens of Yugoslavia will not give in - NATO can destroy many more buildings and bridges, claim more human lives, but it cannot take away our freedom."

British Defense Secretary George Robertson said: "We are now striking at the very heart of his (Milosevic's) bloodstained regime, and we'll do so again and again and again.'"

NATO's Shea said that "any aspect of the power structure is considered as a legitimate target by NATO."

"If I can take the image of the human body," he said, "we will go for the brain as much as we will go for the fingertips."

The 14-month Kosovo conflict has killed thousands of people and driven more than 600,000 ethnic Albanians from their homes. Just over a million people remain in Kosovo, and an estimated 850,000 are internally displaced, according to Shea.