Danny Glover (Flight of the Intruder) is an actor who likes to combine social consciousness and challenging dramatic roles-as he did in films like The Color Purple and the recent To Sleep With Anger. But fans, it seems, like Glover more as an action hero, especially the criminal-clobbering L.A. cop of the Lethal Weapon movies, Roger Murtaugh. ''I was on a plane once,'' the 43-year-old Glover recalls, ''and this guy from Shearson Lehman tells me, totally unsolicited, that Lethal Weapon is his favorite movie. I mean, I've done Places in the Heart, Witness, Silverado...it's strange,'' he says. Glover's fine turns in those more serious films have put him at the top of the list for prominent roles given to black actors, but he claims he doesn't always get what he's after. ''I'm offered the high-profile black roles,'' he says, ''but it's not a case where I automatically get them. There are parts I've wanted to play that Denzel (Washington) and Morgan (Freeman) got. The problem,'' Glover adds, ''is that people (in Hollywood) don't see any difference between us. They don't see any shading between the three black actors. Rick Moranis and Marty Short might be able to play the same part, but there is a difference between Rick Moranis and Mel Gibson. There should be a place for everyone.''