Two trapped whales reversed course and headed back toward shore, frustrating efforts to coax them toward open water, as scientists probed an ice ridge for a weak spot that Soviet icebreakers could attack.

"It's discouraging," federal biologist David Withrow said Monday as the mammals, apparently spooked by a shoal that has stymied progress for three days, retreated about 800 yards. "Why come back here when they know it's open up there?"The California gray whales struggled up for air, tiring quickly as they poked their way through large slabs of Beaufort Sea ice and thick slush left by efforts to carve them a path to freedom.

At one point, the 27-foot-long whale - the smaller of the two - rested the end of its huge snout on the edge of the ice. Blood oozed from a raw spot on its snout, smearing the ice and staining the water.

Biologists called a temporary halt to opening new breathing holes so the whales would have a chance to rest and perhaps seek the open water on their own.

Rescue coordinator Ron Morris of the National Oceanic and Atmospheric Administration remained optimistic.

"They always regress some before they learn," Morris said of the whales. "They'll move."

Meanwhile, specialists determined through soundings that there is about 40 feet of water beneath the pressure ridge, a jumbled mass of ice chunks about 30 feet high and as wide as two football fields.

"There is a lot of water flowing beneath the ridge, which should mean it will be easier (for the Soviet icebreakers) to break through" than had been expected, Morris said.

The icebreakers Admiral Makarov and Vladimir Arseniev were expected to arrive Tuesday.