To the words Tombstone and Wyatt Earp mean anything to Ken Burns and Spike Lee? Apparently not. In the latest Hollywood double play, the Baseball documentarian and Malcolm X director are both pursuing feature films about famed Brooklyn Dodgers infielder Jackie Robinson. First up to bat is Burns' bio, which he'll coproduce with Merchant Ivory for Disney's Hollywood Pictures. ''We're actively going forward with it,'' says the studio's senior vice president Charles Hirschhorn. Although there is still no word on a director or a cast, Hirschhorn expects to release the film by late 1995. Waiting in the bullpen is Lee. He plans to cast Denzel Washington as the legendary Robinson, and is currently conducting research interviews with the player's teammates as well as his widow, Rachel. ''Rachel Robinson turned down (Burns and Disney) because she wasn't sure they were going to make Jackie's story,'' claims Lee, who won't begin filming until early '96. But isn't it inevitable that one of these movies will strike out? ''(Lee's film) means nothing for our project,'' insists Hirschhorn. Spike sees it another way. ''It will be the same as it was between Ruby and JFK,'' he says. ''They'll be Ruby, and we'll be JFK. Ken Burns has his vision, and I have mine. People will know which one will be bogus and which one will be real.''