The concerns were outlined in a report to Congress that was publicly released yesterday, a day after final approval was granted for a pilot program. In the report, the inspector general found fault with plans to inspect Mexican drivers and trucks, which are required to meet the same standards applied to U.S. truckers.

The inspector general also said the Federal Motor Carrier Safety Administration – the Transportation Department agency responsible for administering the program – needed to ensure that state authorities across the United States understand their roles in implementing the program. It noted that several states lack procedures for enforcing regulations that prohibit Mexican trucks from making point-to-point deliveries within the United States, while permitting them to haul cargo back to Mexico.

But in a letter delivered Thursday to both houses of Congress, Transportation Secretary Mary E. Peters certified that the department had addressed all the inspector general's concerns.

Peters also said the program, launched as a one-year demonstration project, is important “for maintaining our relationship with one of our nation's largest trading partners.”

Peters' assurances satisfied congressional requirements for the trucks to start rolling, as first anticipated in the North American Free Trade Agreement, which went into effect in 1994. It proposed to erase rules that limited Mexican trucks to making deliveries within 25 miles of the border.

NAFTA called for an open-border trucking arrangement to be in place by 2000. But U.S. authorities, responding to a chorus of concerns about jobs and safety, withheld approval. The delays drew angry protest from Mexico City, where government officials accused the United States of failing to honor its commitments.

With strong backing from the Bush administration, the pilot program is projected to grow incrementally. It will allow up to 100 Mexican trucking companies to deliver goods anywhere in the United States.

But it continues to face legal challenges north of the border.

The Owner-Operated Independent Drivers Association, which says it represents 155,000 drivers in the United States and Canada, yesterday petitioned the federal Court of Appeals in Washington to block implementation of the program.

The program “creates important safety issues for professional truck drivers who use the nation's highways 24 a day, seven days a week,” the association told the court.

John Hill, Federal Motor Carrier Safety Administration administrator, disputed those concerns.

“This long-awaited project will protect public safety on American highways as we work to both save consumers money and help our economy,” he said yesterday.

Hill also reported that Mexican authorities had cleared the first U.S. trucking company to make deliveries all across Mexico. Such reciprocity was also specified by NAFTA.