SAN FRANCISCO  —  The Bush administration urged a federal appeals court Thursday to let Mexican cargo trucks cross the border and freely travel anywhere in the country, arguing that to do otherwise could strain diplomatic relations between the U.S. and Mexico.

The Teamsters Union on Wednesday asked the 9th U.S. Circuit Court of Appeals to stop the program, which could go into effect as early as Saturday.

The union argues that the administration plan, which would let as many as 100 registered Mexican trucks deliver their cargo anywhere in the country for the next year as part of a "demonstration program," would endanger public highways because safety issues have not been resolved.

But in its filing Thursday, government lawyers said the trucks enrolled in the program meet U.S. trucking regulations and the program is a necessary part of the North American Free Trade Agreement.

"Participating Mexican carriers must comply with all legal requirements governing operations of domestically owned carriers, and in some cases stricter requirements," wrote Assistant Attorney General Peter Keisler.