Facing a chronic shortage of foreign troops for peacekeeping missions, President Bush has decided to launch an international drive to boost the supply of available forces -- a move that if successful could relieve some of the pressure on U.S. soldiers to join such operations, defense officials said. A plan approved by Bush earlier this month calls for the United States to commit about $660 million over the next five years to train, equip and provide logistical support to forces in nations willing to participate in peace operations.