Among the countless perversities and mysteries of TV, the slighting of ''Scrubs" has been notable. Why hasn't this sly sitcom been an Emmy magnet during its four seasons? How come viewers haven't made it a Nielsen hit, or at least a cult sensation that gets fetish pieces in Entertainment Weekly? Why does NBC shuffle it around the schedule every year like a dung-puck, withholding season five until a gap happened to open up in the Tuesday lineup?
Yes, this is another tribute to the underappreciated hospital sitcom, which returns tonight with two episodes at 9 on Channel 7. ''Scrubs" deserves it. There is something giddily inventive about producer Bill Lawrence's laugh-track-free show, which crams its weekly 22 minutes with visual, verbal, and aural comedy, not to mention a bit of drama. With its density of material, it doesn't waste a second of time upon the electronic stage. ''Scrubs" operates like a tight, ''Simpsons"-esque animated series, and ''Arrested Development" probably wouldn't be so rich and hyperactive if ''Scrubs" hadn't paved the way. At a time when too many TV writers cruise on automatic pilot, there is nothing lazy or clone-like about ''Scrubs."