WASHINGTON (AP) - Judge Sandra D. O'Connor of the Arizona Court of Appeals has emerged as a leading candidate to succeed Justice Potter Stewart on the U.S. Supreme Court, the Washington Post reported today. "She hasn't been chosen yet. but she's close," the newspaper quoted one unnamed Reagan administration source as saying. The Post said Mrs. O'Connor, 51, was interviewed for the vacancy by an administration official and was believed to be the only potential nominee to be interviewed. In another development, the New York Daily News quoted Reagan administration sources in today's editions as saying that U.S. District Judge Lawrence W. Pierce, a 56-year-old black. is also being considered for the high-court seat. Administration officials said Mrs. O'Connor is on a "short list" of leading candidates - most of them women - for Stewart's seat, which becomes vacant when he retires Friday, according to The Post. During his campaign last year. President Reagan said he wanted to name a woman to one of the first vacancies on the nine-member court. The White House, however, has kept open the possibility that a man could be named to succeed Stewart. Until now, one of the women mentioned most often as Stewart's likely successor has been Cornelia Kennedy of Detroit, a member of the 6th U.S. Circuit Court of Appeals. The Post said Mrs. O'Connor has support from both of Arizona's senators, Republican Barry Goldwater and Democrat Dennis DeConcini, a member of the Senate Judiciary Committee.