Sen. Lloyd Bentsen says the Bush administration could boost congressional support for a free trade agreement with Mexico by explaining how it will deal with labor and environmental concerns.

Bentsen, D-Texas, has asked President Bush to outline by May 1 how he would address disparities in wages and environmental regulations between the two countries during negotiations to lift trade barriers throughout North America.The deadline is nearing for Congress to decide whether to give the administration "fast-track" authority to negotiate a non-amendable trade agreement with Mexico and Canada. Critics have mounted an aggressive campaign to derail the talks.

Bentsen, chairman of the Senate Finance Committee, said he plans a hearing in April on a resolution to kill the two-year fast-track extension.

Asked Thursday whether he thought the administration was doing a good job lobbying Congress to extend the fast-track, Bentsen said: "They'll have done a better job when they answer some of the questions I've asked them." He supports the extension.

Bentsen's counterpart in the House, Ways and Means Committee Chairman Dan Rostenkowski, D-Ill., has also sought answers to those questions. On Wednesday, House Majority Leader Richard Gephardt, D-Mo., announced his support for the free trade agreement was contingent on "the inclusion of assurances that American jobs will not be lost in droves."

Opponents of the fast-track extension, including textiles, consumer activists, environmentalists, organized labor and some farm groups, claim a free trade agreement could prompt an exodus of jobs to Mexico, where wages are a fraction of U.S. levels.

Critics also claim lax enforcement of environmental regulations south of the Rio Grande would give companies that relocate in Mexico a competitive advantage over those that remain in the United States. Others fear that Mexican produce treated with pesticides that don't meet U.S. standards would enter the country.

Advocates say lifting tariffs and other trade barriers will create U.S. jobs.