One of three trapped whales was presumed dead Saturday, but its companions inched toward open water as Eskimos cut a string of breathing holes and a helicopter battering ram smashed a path through thick ice.

"They certainly have a very good fighting chance in their battle to escape," David Withrow, a federal marine mammal biologist, said Saturday.However, a huge ridge formed by colliding ice masses stood in the way of a breakthrough for the California gray whales, members of an endangered species. The big marine mammals were about four miles from open water.

A second ice-smashing Skycrane cargo helicopter was standing by two hours away in Prudhoe Bay in case rescuers decided a second concrete ice-bashing "bullet" was needed.

And at White House direction, the Air Force assigned the largest aircraft in its inventory - the C-5A Galaxy - to ferry more equipment from Prudhoe Bay to Barrow, Air Force Maj. Doug McCoy said Saturday.

The whale nicknamed Bone disappeared beneath the foot-thick ice Friday afternoon. By midnight Friday, rescuers on the ice near this small Eskimo town on the Arctic Ocean had given up hope Bone might rejoin the others.

North Slope Borough biologist Geoff Carroll said the whale was presumed dead.

"Everyone is sorry to hear about the whale, but I don't think it was totally unexpected," Carroll said Saturday. He had told reporters earlier the whale was the weakest of the three and had some respiratory problems.

Bone, Crossbeak and Bonnet became trapped at a small breathing hole in unseasonably heavy ice more than two weeks ago during their annual migration south. Open water was too far away for them to reach it without surfacing to breathe.

The missing whale got its name because skin on its snout had been rubbed to the bone by the rough ice surrounding the breathing hole. That condition may have led to Bone's death, said biologist Craig George.

"Once they get a bone infection, they go pretty quick," George said.

The whale's body probably sank to the bottom but may float in a few days because of gases from decomposition, George said. "We'll either find it or a (polar) bear will," he said. Polar bears feed on whale carcasses.

Something will have to be done about the ice ridge, and soon, if the remaining whales are to be freed, said Col. Tom Carroll, in charge of the Alaska National Guard's two Skycrane helicopters on loan for the rescue.

"We looked for an alternate route (bypassing the ridge) and didn't find it," he said. "If there's no way through it, it will have to be tackled early while the whales still are some ways from it."

The ridge lies about a quarter-mile from an area of open water leading to the open sea.

The ridge was believed to be too thick to be punctured by the helicopters' five-ton, steel-reinforced concrete hammers, and local ice specialists were assessing the situation Saturday, said Geoff Carroll. "I think we're going to blast," he said.