Most television shows that last a really long time have to grow and change in order to survive. Not so "Law & Order," which airs its 300th episode tonight and which hasn't changed much of anything.

Well, the cast has changed, of course. Considerably. None of the original actors remains, and the show has been a veritable revolving door since its debut in September 1990.

Frankly, none of that matters all that much, because "Law & Order" has never been a show about its characters. Oh, we get glimpses of them from time to time, but they're secondary to the stories. Which may help explain why "Law & Order" has lasted as long as it has.

"CSI" may be the hottest procedural drama on the air right now, but "L&O" is the oldest. The format remains much the same from week to week: The police detectives investigate a murder, the most obvious theory turns out to be a false lead, there's a twist of some sort that leads the officers to the real killer, they turn the case over to the prosecutors, there are some dramatic courtroom scenes and the verdict comes in.

Which is not to say the episodes are all alike. The format varies a bit from week to week: Sometimes the wrong person is arrested; the bad guys sometimes go free. But it all falls within the "Law & Order" parameters, which have kept the show a success for 13 seasons and 300 episodes, making it the fifth longest-running hourlong drama in TV history. The show has already been renewed for two more seasons.

And "L&O" has lived for 13 seasons on ripped-from-the-headline plots. Famous (or infamous) cases are adapted for the series, always with a twist.

Tonight, following a repeat at 7 p.m., the 299th episode at 8 p.m. features a series of murders — including one in which a distraught wife runs over her cheating husband with her car. And the 300th episode at 9 p.m. revolves around the death of a baby who is held out a hotel window by his famous father. It turns out the famous father has a history of being accused of child sexual abuse, and, in lieu of a way to charge him with the crimes, the prosecutors charge the parents who let their kids have contact with the guy.

Bet Michael Jackson will love this one.

ENTERPRISING: UPN's "Enterprise" debuted last season with a strong concept, a fine actor (Scott Bakula) in the captain's chair and a lot of promise . . . on which it has not delivered. It's not that it's an awful show, it's just, well, boring.

So they're going to try, try again to juice things up. In the second-season finale (7 p.m., Ch. 24), a few million Earthlings are killed by an alien weapon. And the Enterprise is sent into a dangerous region of space to battle this new foe.

It looks like a promising idea. But, at this point, it's pretty hard to get your hopes up too high for "Enterprise."

E-mail: [email protected]