The youngest son of the former Prime Minister Pierre Trudeau was swept into a mountain lake by an avalanche in British Columbia on Friday and is presumed drowned, police officials said today. Heavy snow has forced rescue teams to suspend their search.

The young man, Michel Trudeau, 23, was trying to make his way out of the Kokanee Glacier Provincial Park, about 100 miles north of the Washington-Idaho border, when he and three friends were caught in a snowslide that pushed them down the mountain and swept two of them into the frigid waters of Kokanee Lake, the police said.

Skiers who witnessed the avalanche hiked to a nearby town and called the police. A rescue helicopter arrived Saturday morning and picked up three of the skiers but Mr. Trudeau was not found.

Sgt. Russ Grabb, a spokesman for the Royal Canadian Mounted Police, said divers would be sent to search the lake once the weather clears and the snow surrounding the lake can be stabilized by dropping explosives from a helicopter.