Two Soviet icebreakers were leaving for home on Friday after they finished smashing through the remaining 300 yards of an ice pack that had trapped a pair of California gray whales, the U.S. National Guard said.

U.S. scientists said they would not know until dawn (about noon MDT) whether the final punch through the ice by the 496-foot Vladimir Arsenev succeeded in freeing the two whales so they could make a normal migration to warmer waters.The Soviet ships, in an unusual joint venture with the United States, arrived here on Wednesday and quickly broke through a solid ridge of ice and cut a channel that the big mammals were able to swim into after nearly three weeks of captivity under the ice.

But the whales lingered in the channel so long that the slush and ice chunks began re-freezing the pathway to unfrozen seas.

On Thursday, Eskimos dug some 50 breathing holes in the ice in a path toward the ocean and lured the whales about 300 yards from the edge of the ice pack, said Ron Morris, coordinator of the rescue effort for the National Oceanic and Atmospheric Administration.

He said the Arsenev planned to make another two or three passes at the ice before heading for its home base in Vladivostok.

The icebreaker, which was accompanied by the 440-foot Admiral Makarov on the mission made at the United States' request, planned to cut into the ice as close as 10 to 20 yards from the hole where Eskimos had lured the whales, said NOAA Adm. Sigmund Petersen.

"We feel we're going to be successful in freeing the whales," said Petersen.

Scientists said they expected the mammals to swim into what is known as a "lead," a wide and long strip of unfrozen water found between sheets of ocean ice. By swimming from lead to lead, the whales should be able to finish their winter migration, they said.

Scientists said it was possible that the juvenile whales, which they had named Crossbeak and Bonnet, would be gone by daylight and might never be seen again.

Petersen said the Soviet crews had been at sea for six months and were anxious to return home.

U.S. Coast Guard Capt. Jim McClellan spent two days aboard the Soviet ships, which were visited by several delegations of Americans, and he praised the Soviet crew for their professionalism. The captain of one vessel assured him the Soviet government would not send a bill for the operation, he said.

He said the captain estimated the cost at 30,000 rubles a day for the seven to 10 days the diversion to the United States had taken. The whale-rescue effort cost the Americans more than $1 million.