WASHINGTON (AP) _ More than half the Senate asked President Bush on Thursday to pressure Canada to renew an expiring trade agreement that restricts imports of Canadian softwood lumber into the United States.

Once the 5-year-old Canada-U.S. softwood lumber agreement setting a ceiling on duty-free shipments expires April 1, more cheap lumber from Canada will threaten to put U.S. sawmills out of business, 51 senators said in a letter to Bush.

``Doing nothing, or extending the current agreement for a short period of time, will only provide advantages for the Canadian industry and destroy our domestic softwood industry,'' Sen. Max Baucus of Montana, the senior Democrat on the Senate Finance Committee, told reporters.

The letter, spearheaded by Baucus and Republican Sens. Larry Craig and Mike Crapo of Idaho, asks Bush to meet soon with Canadian Prime Minister Jean Chretien to strike a new deal.

The U.S. trade representative's office did not immediately return phone calls seeking comment on how the administration might respond to the senators' request. The Clinton administration had indicated it would not seek an extension of the pact.

Canada now supplies about a third of the softwood lumber used in the United States.

U.S. homebuilders oppose extending the quotas, claiming the resulting higher lumber prices have added about $1,000 to the cost of a new house.