Yet light trucks pose significant problems - and not just prodigious gasoline consumption.

In this instance, Mr. Duffy denies that the truck posed much of a hazard.

A year ago, the technical investigators on the case told Mr. Pena that they had found that the trucks did not pose an unreasonable risk.

As a result, he said, employing critical legal language, the trucks posed an "unreasonable" risk of death or injury.

Mr. Pena did not answer directly when asked at a briefing with reporters in Washington today if he still believed the trucks posed an unreasonable risk.

The trucking industry argues that bigger trucks will increase efficiency, decrease costs for customers and pose little safety hazard.

The Administration, which negotiated the agreement two years ago, is now fearful that the trucks could pose safety hazards and spur trade in illegal drugs.

Jeffrey R. Miller, the highway safety agency's acting administrator, said light trucks and multipurpose vehicles have posed a relatively minor safety problem.

Largely missing from research on the dangers light trucks pose to cars are crash tests and studies by universities and private companies.

Light trucks pose a danger because they are heavier than cars, ride higher off the ground and have stiff frames, Mr. Hollowell said.