TIRANA, Albania (AP) _ An Apache helicopter crashed during a nighttime training mission in northeast Albania and exploded in a fireball early today, killing two U.S. airmen _ the first American fatalities in the 6-week-old NATO air campaign.

It was the second Apache destroyed in a crash since the 24 specially equipped anti-tank helicopters were deployed in Albania two weeks ago.

The cause of the crash was under investigation, but the Pentagon said there were no indications of hostile fire though the flight was near the borders with Macedonia and Yugoslavia.

Lt. Col. Garrie Dornan, a spokesman for the U.S. task force that includes the Apaches, said the helicopter crashed in remote, rugged, mountainous terrain at 1:30 a.m., about 46 miles northeast of Tirana's airport.

Dornan said the pilots were dead when the first rescue team arrived within 15 minutes.

The Army withheld the pilots' names pending notification of next of kin but President Clinton, speaking to U.S. troops today at an air base in Spangdahlem, Germany, lamented the loss of "two brave Americans."

"Today, we grieve with their families and pray for them," Clinton said.

Maj. Toni Kemper at the U.S. European command in Stuttgart said both victims were trained pilots but when they fly in the Apache together, one acts as the pilot and the other as gunner.

She said the question of whether the two were wearing night vision goggles is part of the investigation and can't be answered right now. She also said the pilots' bodies would be flown through Ramstein Air Base in Germany en route home but it was not clear when.

Dornan told reporters at the Tirana airfield where the Apaches are based that the crash would not affect training or the still-secret schedule for deploying the heavily armed helicopters in combat.

"This will not hinder the timeline _ there's no delay, no aircraft grounded," he told a news conference. Dornan said the mood among the pilots was "mournful."

Dornan declined to speculate on the cause of the crash, saying it burst into flames and that there was a "fireball." He said it appeared some of the ammunition on the chopper had exploded and was destroyed.

The Apache training was deliberately rough in order to prepare the pilots.

"We train hard so when we go into combat we're prepared. We can never eliminate risk from this business," he said. "We are flying in total blackout conditions, we're flying in difficult terrain."

Gen. Hugh Shelton, chairman of the Joint Chiefs of Staff, said of the crash: "We must never lose sight of the fact that our military men and women operate in a very hazardous environment day in and day out in support of America's national security."

The Apaches are expected to be deployed soon against Yugoslav troops in Kosovo province, where more than 675,000 ethnic Albanians have been forced to leave their homes since March.

Last week, another Apache went down in flames, also while on a nighttime training mission in Albania. Its crewmen escaped with cuts and bruises.

Dornan said there appeared to be no link between the two crashes.

The $14.5 million Apaches, renowned for their tank-killing abilities, carry a 30mm gun, 76 2.75-inch rockets and 16 Hellfire missiles.

They fly up to 189 mph, were first used in 1989 in Panama, in Iraq in 1991 to knock out Iraqi tanks during the Desert Storm conflict, as well as in Bosnia.

The Apaches are a high-maintenance aircraft that require ground support at their bases, are known for their ability to fly at night and in bad weather and hide in rough terrain such as the Balkans but are vulnerable to ground fire because they stay low and fly relatively slow.

(Copyright 1999 by The Associated Press. All Rights Reserved.)

APTV-05-05-99 0940MDT