WASHINGTON -- The US Senate dealt President Clinton his first legislative defeat yesterday, voting to write into law the Bush administration's policy prohibiting people infected with the AIDS virus from immigrating to the United States. The defeat came despite Sen. Edward M. Kennedy's spirited battle in defense of the president's commitment to lift the prohibition. The Senate voted, 76-23, to prevent people infected with the HIV virus, which causes AIDS, from immigrating, after defeating by a 56-42 vote an amendment by Kennedy that would have kept current federal policy in place for 90 days but left Clinton free to change...