THE HIGHEST-RANKING official to flee China since the crackdown on the pro-democracy movement has been ousted from the national legislature and denounced as a traitor, an official report said. The report confirmed for the first time that Xu Jiatun, China's top representative in Hong Kong, fled to California last year without official authorization . . . A HIGH SCHOOL SOPHOMORE in Providence, R.I., filed suit in federal court to challenge a Rhode Island Interscholastic League rule that bars him from joining his school field hockey team because he is male. Brian Kleczek, who is being represented by the American Civil Liberties Union, argues in the case filed Thursday that the league policy preserving field hockey for girls exclusively violates the state Equal Rights Amendment.