Is there a chance for the Rocket's third stage in pinstripes? Not likely, says Hank Steinbrenner. So if embattled righthander Roger Clemens, who is fighting to restore his reputation after the allegations about him in the Mitchell Report, pitches a 25th season, it is probably not going to be in the Bronx. "I'm not signing Clemens," Steinbrenner, the Yankees' Senior Vice President, said in a telephone interview yesterday. He said the Yanks are not looking for rotation stopgaps - like they were last season - because they are so enamored of their young starting pitchers. And Steinbrenner feels the Yanks already have a strong mentor to the young arms in Andy Pettitte, whom Steinbrenner praised for his "veteran leadership. "Andy is (signed) for one year, and he's only 35 and he knows how to pitch in the big games," Steinbrenner said. "Roger does, too, but let's face it, he's going to be 46 (in August)." "Pettitte is just as good with the young pitchers, though Clemens was great with the young kids last year. I don't think Roger is going to come back anyway."