WASHINGTON, D.C. — President Bush has ordered plans for temporarily disabling the U.S. network of global positioning satellites during a national crisis to prevent terrorists from using the navigational technology, the White House said on December 15, according to a report by the Associated Press. Any shutdown of the network inside the United States would come under only the most remarkable circumstances, said a Bush administration official who spoke to a small group of reporters at the White House on condition of anonymity, according to the report. The GPS system is vital to commercial aviation and marine shipping. The president also instructed the Defense Department to develop plans to disable, in certain areas, an enemy´s access to the U.S. navigational satellites and to similar systems operated by others. The European Union is developing a $4.8 billion program, called Galileo. The military increasingly uses GPS technology to move troops across large areas and direct bombs and missiles. Any government-ordered shutdown or jamming of the GPS satellites would be done in ways to limit disruptions to navigation and related systems outside the affected area, the White House said. In May 2000, President Clinton abandoned the practice of deliberately degrading the accuracy of civilian navigation signals, a technique known as “selective availability.´´ The White House said it will not reinstate that practice, but said the president could decide to disable parts of the network for national security purposes. The White House said the policies were aimed at improving the stability and performance of the U.S. navigation system, which Bush pledged will continue to be made available for free. The U.S. network is comprised of more than two dozen satellites that act as beacons, sending location-specific radio signals that are recognized by devices popular with motorists, hikers, pilots, and sailors. Bush also said the government will make the network signals more resistant to deliberate or inadvertent jamming.