WASHINGTON -- Two Japanese automakers have asked the Commerce Department to extend reduced duties they pay on imported parts for their American-made cars.

The companies want to expand their factories in the United States without paying higher tariffs on the additional parts they will need to import.

Since opening U.S. factories in the 1980s, Toyota Motor Corp. and Nissan Motor Co., like Detroit's Big Three automakers, have held an exemption that lets them pay duties of no more than 2.5 percent on parts they import for assembly. The standard duties for auto parts range from 3.1 percent to 11 percent.

The Japanese companies' request to keep paying the lower duties even as they nearly double the number of parts they import presents the Bush administration with a difficult choice: giving Japan favorable trade treatment amid friction over its large trade surplus or discouraging job-creating Japanese investment in factories here.