President Bush on Friday signed into law measures to upgrade airport security and to encourage volunteerism and community service. Bush signed the bills as he hurried to finish domestic business before an eight-day foreign trip. The Aviation Security Improvement Act of 1990 directs the government to develop guidelines to warn passengers of terrorist threats. It implements safety recommendations of the Commission on Aviation Security and Terrorism appointed by Bush after the bombing of Pan Am Flight 103 over Lockerbie, Scotland. The bill sets regulations on airport use of metal detection devices. It requires airlines, airports and travel agents to relay any security threat immediately to government officials. Airline and airport employees with access to security areas will have to undergo background checks and new training. In signing the bill, Bush said he had reservations about a provision requiring the State Department to negotiate agreements with other nations to achieve the enhanced security measures at foreign airports. Bush said he believed that provision intruded on his presidential authority to conduct foreign policy and said he would direct officials to interpret it so as not to conflict with that authority. The National Community Service Act of 1990 provides $287 million for community service programs, including $5 million to begin a Thousand Points of Light Foundation to encourage volunteerism, taking its name from Bush's phrase for volunteers. It provides money for programs encouraging youth community service through schools or community organizations; grants to state education agencies; expansion of youth corps teams for such projects as environmental cleanup and helping the poor; and a test program for a civilian national service corps that would provide $5,000 in education assistance in return for a year's full-time service at a subsistence wage. Bush signed the measure despite attacks by Republicans that it included wasteful spending at a time when the government was raising taxes, and budget constraints prevented full funding existing programs for children and the poor. Bush also on Friday signed the Excellence in Mathematics, Science and Engineering Education Act to establish a variety of fellowships, training programs and grants to foster and improve education in those fields. The bill authorizes $150 million for such programs in 1991. The president vetoed the Indian Preference Act of 1990, which would have established a program to direct contracts and grants to Indian enterprises. Bush said the bill ``would impose new, expensive, and often duplicative program responsibilities'' on the Interior Department, which administers Indian reservations. Bush said in a statement that he supports the bill's goals and is ``committed to helping alleviate the widespread unemployment and underemployment on Indian reservations.'' He said the bill's issues ``deserve a full airing in both Houses of Congress. He said he would direct Interior Secretary Manuel Lujan to take steps to address problems with contracting programs involving Indian enterprises. Bush took the action before departing Friday night for Prague, the first stop of an eight-day trip that will also take him to Paris, Saudi Arabia and Egypt.