A New York judge's libel ruling Thursday against the Prodigy online service sent chills through the rest of the online world, but -- according to the judge himself -- Prodigy may have more to worry about than its competitors. State Court Judge Stuart Ain allowed Stratton Oakmont Inc., an investment bank, to proceed with a $200 million libel suit. The bank holds Prodigy responsible for statements about it made by Prodigy subscribers on the service's electronic bulletin board last fall, which the bank contends were libelous. The implication is that theburgeoning on-line information industrybears liability for any fabrication or obscenity carried on its communications channels. Ironically, the judge said Prodigy is more vulnerable to libel claims than other services because it has booted obscene messages off its bulletin boards and scrutinized subscriber speech. ButTIME senior technology editor Philip Elmer-DeWittsays other online providers shouldn't feel safe, since the Supreme Court's conservative membership may tend to side against them in such matters.