The public disappearance of Soviet Politburo member Konstantin Chernenko may not be Kremlin intrigue after all. So, at least, says a Soviet official, who maintains Mr. Chernenko has merely been ill. The longtime protege of the late Leonid Brezhnev was once seen as a prime contender to succeed him. But he has been inexplicably absent from public functions in recent weeks, Monitor correspondent Ned Temko writes. Mr. Chernenko's appearance at the coming May Day celebrations depended on the opinion of doctors, said the source, who is senior enough to know details of Chernenko's status, but not a member of the Communist Party's Central Committee. Mr. Chernenko continues to do some work, the source added.