President Bush's chief economic advisor, Glenn Hubbell, is on the last leg of a campaign to garner support for giving the White House broad authority to negotiate trade agreements. The House of Representatives is scheduled to vote on the issue Thursday. The outcome is uncertain. The merits of free trade are not in dispute. But the issue before Congress is mired in politics and special interests.

The so-called Trade Promotion Authority bill, or TPA, would allow the president to negotiate trade agreements with other countries that Congress would be able to approve or vote against, but not amend.

Mr. Hubbell, the chief economic advisor for the White House, addressing the Council on Foreign Relations, a private group, said Congress should not be allowed to renegotiate a trade deal. It goes to the heart, he argued, of the president's credibility in dealing with foreign countries. "Now, obviously, Congress still has an important, final and rightful say in whether the U.S. signs a trade agreement. What TPA provides the president is the maximum flexibility to give the United States additional credibility and bargaining power in the international community," he said.

The bill presents big problems for many Democrats, who want trade agreements to contain binding labor and environmental protections. It also poses difficulties for representatives from steel, agriculture and textile-producing regions of the United States. They are looking for some sort of protection for their import sensitive industries.

The president's chief economic advisor said those concerns may be valid. But he argued the Trade Promotion bill, also known as fast-track authority, needs to keep its focus on trade. "And it sends a signal to other countries that the U.S. is united in active engagement in trade negotiations that will benefit all participating countries," he said.

The White House is eager to get the bill passed before the next round of World Trade Organization talks, due to begin shortly. Supporters said they are prepared to address the labor issue by voting on a separate bill renewing a program to help retrain and relocate U.S. workers who lose their jobs because of increased imports.

The issue of "fast-track" trade authority bedeviled the previous administration. President Clinton persuaded House leaders in 1997 to cancel a vote at the last minute, when it was clear there was not enough support for passage.