"While our country's future trade policies are debatable, the right of Congress to participate actively in setting those policies is not," said Sen. Mark Dayton, D-Minn., a leading advocate of the proposal, which cleared on a voice vote.
The vote was a major blow to President Bush, who has threatened to veto the underlying "trade promotion authority" bill if the Dayton-Craig amendment was attached to the trade promotion measure.
Earlier, the Senate the rejected an effort to kill the amendment by a vote of 38-61.
The developments unfolded as lawmakers debated legislation to give Mr. Bush the authority to negotiate international agreements subject only to a yes-or-no vote in Congress.
Presidents have had such authority for much of the past quarter-century. But it lapsed in 1994. The GOP-controlled Congress refused to renew it during the Clinton administration.
Mr. Bush, echoing arguments by Clinton and other former presidents, says the authority is essential as the United States enters a new round of World Trade Organization talks.
But the vote on the proposal by Dayton and Sen. Larry Craig, R-Idaho, reflected concern among lawmakers that while international trade is a boon to the economy, it also harms the steel, textile, farm and other industries.
Craig, a member of the Senate Republican leadership, and Dayton would amend the presidential authority to give Congress the power to delete from any fast-track deal any part of the agreement that affects laws protecting U.S. industries from foreign subsidies and dumping.
But Commerce Secretary Donald Evans, in a letter to Sen. Max Baucus, D-Mont., who chairs the Senate Finance Committee, said the amendment derails fast track, or trade promotion authority, "without justification." He said he would "strongly recommend to the president that he veto legislation that included this amendment."
He said the legislation already directs the president to "preserve the ability of the United States to enforce rigorously its trade laws." If Craig-Dayton passes, he said, "other countries will refuse to discuss their own sensitive subjects, unraveling the entire trade negotiation to the detriment of U.S. workers, farmers, and consumers."
The letter was also signed by Agriculture Secretary Ann Veneman and U.S. Trade Representative Robert Zoellick.
White House press secretary Ari Fleischer said the president "understands the concerns made by his cabinet members." He said the veto threat was made because the amendment "would seriously undermine the cause and the purpose of free trade."
Craig, who has rejected administration requests that he withdraw the amendment, said it would strengthen the president's negotiating hand by sending a clear message to U.S. trading partners that Congress stands behind U.S. trade remedy laws.
But at a news conference Tuesday, leaders of the business community joined senators in warning that the amendment was a "poison pill."
"It essentially emasculates trade promotion authority and renders all of our work useless," said Jerry Jasinowski, president of the National Association of Manufacturers.
Sen. Phil Gramm, R-Texas, who last week helped work out a compromise on language sought by Democrats to increase benefits for trade-dislocated workers, said Craig-Dayton was a "bipartisan protectionist amendment" that would "destroy our ability to negotiate reductions" in trade barriers.