The Bush administration announced Monday its plans to extend for two years an unpopular Mexican cross-border trucking project required by a trade treaty, setting up a bitter turf battle with Congress.

The program, which allows up to 100 Mexican trucking companies to operate in a 25-mile zone along the U.S. border, was originally billed as a one-year trial and was set to expire Sept. 6.

Before leaving for its August recess, the House Transportation and Infrastructure Committee approved a bill last week that would stop the Transportation Department from continuing with the pilot program.

“When Congress reconvenes in September, I intend to move our bill as quickly as possible, and make certain that the voice of Congress is heard loud and clear at the Department of Transportation, and that this program is finally shut down,” Committee Chairman James L. Oberstar, D-Minn., said in response to the administration’s move.

Allowing Mexican trucks to operate in the United States has drawn stiff opposition from Congress, which ordered the administration to stop funding the program in the fiscal 2008 omnibus spending law. Lawmakers have expressed concerns about safety and the environmental impact of the program.

But the administration has refused, citing the North American Free Trade Agreement — which created a framework for the United States and Mexico to further open their roadways to each other’s trucks — as well as a 2004 Supreme Court case allowing the administration to give Mexican truckers access to U.S. roads.

The administration has warned that if the program is blocked, Mexico could retaliate and impose fees and tariffs on U.S. goods.

According to the Transportation Department’s legal counsel, the amendment barring establishment of a cross-border demonstration project does not prevent the administration from proceeding with a program that already was under way.