'Law & Order' keeps on going and going . . .

After 15 years and more than 600 episodes in four different series, "Law & Order" can still suck you in.

You sit down and start watching an episode and it's hard to pull yourself away before you find out whodunit and why. Which is pretty astonishing when you consider that the original series — "the mother ship," as creator/executive producer Dick Wolf likes to call it — airs its 355th episode on Wednesday (9 p.m., Ch. 5).

Much has been made over the years about the many cast changes the show has gone through, but that's nothing compared to the huge number of people involved behind the scenes. To date, about 100 different writers and 50 different directors have been credited on the show.

Wolf has always been at the top of the "Law & Order" command structure, but a variety of different executive producers — show runners — have been in charge. And there's a new team this year — Walon Green has worked as a writer/producer on the show off and on from the start, but his credits go back to "Hill Street Blues" and include "ER" and "NYPD Blue." Nicholas Wootton is another "NYPD Blue" alumni who executive produced "Blind Justine" last season.

"I think we're looking at a new generation of writers on the show that can, hopefully, put it past my stated goal of beating 'Gunsmoke,' " Wolf said.

That seems pretty much a given at this point — even though "Law & Order" has to run five seasons beyond this one to surpass 20 seasons of "Gunsmoke" as TV's longest-running drama.

But it's not like the new writers and producers are messing with the formula that has made "Law & Order" work for all these years. Viewers know what they're getting no matter what season they tune in to, whether it's new episodes on NBC or constant repeats on cable.

Wednesday's episode follows a familiar pattern. We see the aftermath of a crime at the top of the episode, but as the investigation begins, it turns out that the murder is rather quickly solved. However . . . that investigation leads us to another crime (or series of crimes) that takes an issue that's ripped from the headlines (in this case, forced sterilization) and weaves a story around it.

Longtime fans will recognize the defense attorney — Richard Brooks returns as Paul Robinette, the show's original No. 2 assistant district attorney (who left the series in 1993).