MORE THAN THE SUM OF ITS BODY PARTS HUMOR, DRAMA, RELATIONSHIPS HAVE TURNED `NCIS' INTO A RISING HIT.

Byline: David Kronke Television Writer

On a soundstage tucked within a Santa Clarita industrial complex, cast members of CBS' ``NCIS'' are rehearsing a fairly simple scene.

Mark Harmon as Special Agent Jethro Leroy Gibbs, Sasha Alexander as former Secret Service Agent Kate Todd, Michael Weatherly as agent/classroom troublemaker Tony DiNozzo and Sean Murray as newbie computer geek Timothy McGee theorize on the disappearance and fate of a missing naval petty officer.

All is going smoothly when Alexander, almost to herself, says, ``We're gonna finish this in no time.''

As one, her colleagues and surrounding crew members react with mock outrage.

Alexander has breached one of the production's cardinal rules - never speculate on a scene's shooting length, lest you jinx it. Something called the ``Dobbie board'' - merely a stick with its moniker scribbled upon it, named after the crew member who first committed the offense, attached to a string - is produced.

Weatherly hoists the petite actress upon her character's desk as the string circles her neck and a Polaroid camera appears to immortalize her transgression as laughter echoes through the cavernous edifice. A wall on ``NCIS' '' stage memorializes those who preceded Alexander in this breach of etiquette.

Work on the ``NCIS'' set belies the tension-filled world of high-stakes network television. ``NCIS'' (the letters stand for Naval Criminal Investigative Service) is a quiet hit going mainstream. In its second season, it has become the most popular program on Tuesday nights (``American Idol,'' returning tonight, likely will change that).

Its audience has increased by 2 million this year, and a whopping 33 percent in network TV's all-important 18-to-49 demographic. All earned the old-fashioned way, through solid storytelling and, most important, colorful characters.

Despite good reviews, ``NCIS'' was initially dismissed as both a spinoff of military drama ``JAG'' (also created by Don Bellisario) and a copy of ``CSI,'' but has emerged as something significantly more - a genuinely funny crime drama in which viewers are lured more by character interactions than the mysteries' plot twists. The production's behind-the-scenes playful camaraderie is vividly apparent in what shows up on the air.

``This show isn't cooked up by a committee of people trying to decide what will meet with the approval of the audience,'' says Weatherly. ``The title (with its ``CSI'' echo) might have been cooked up - (but) by the Department of Defense.

``It's really an office drama,'' he continues. ``We bitch and moan the same way anyone who works at a pharmaceutical company does around the water cooler. We're not superheroes or fashion icons, it just happens that what we do is interesting. But mostly we're just bitching and moaning about things.''

``This goes all way the back in style to 'Magnum, P.I.' '' says Bellisario, referring to the first hit series he created a quarter-century ago. ``I tell writers our show is about what happens in the cracks of the regular shows. 'NCIS' is not about following forensic procedure, it's about the characters quipping back and getting into little arguments.''

Bellisario - whose visage is among those on the squad-room set's ``10 Most Wanted'' wall - says he pleaded with the network not to market the series as a ``JAG'' spinoff. ``Which they did,'' he laments. ``I'm probably only the creator of a series who said, `Please don't put ``By the creator of'' on a billboard.'

``I've worked with the promotions people to play up the humor of the show,'' he adds. ``When I saw the photos of the cast, I thought they could be those of any show on TV - forensics, stern expressions, an 'Aren't we cool?' mood. This cast is loose, they're having fun, and the photo and the promos should express that.''

``What distinguished the script for me was character and the humor - both jumped out,'' says Harmon, a man whose hands proffer both a firm handshake and, later, a bunch of fresh grapes for anyone in his vicinity. ``Initially, I was attracted by his name - Leroy Jethro Gibbs - turns out it's Bellisario's dad's best friend growing up in Pennsylvania. There was a moment where that name changed from one draft of the first script to the next, and I called up and said, 'Don't!' So it went back.''

Harmon notes that Bellisario is a stickler for character nuance, recalling with a chuckle that when a crew member placed an authentic NCIS coffee mug on caffeine addict Gibbs' desk, ``That lasted one day.''

``I went through the roof,'' Bellisario agrees with a laugh. ``It's in the details to me. Gibbs drinks out of a Starbucks or Coffee Bean cup. Strong, black.''

And the cast responds with equal dedication to capturing their characters. David McCallum, who plays medical examiner Donald ``Ducky'' Mallard, has done so much research into coroners that, Bellisario jokes, ``He's probably slipped into a morgue and dissected some bodies.''

``You do have to be careful'' about obsessive research, McCallum concedes. ``You can be at a dinner party, talking about how you section a brain - you don't want to put people off. But I find they're interested - people will say, 'Gross!' - and then keep asking questions.''

Each cast member has specific memories of the scene in which his or her character's place in the series became clear, and it's usually through deviating from the original script. Interestingly, Bellisario agrees with their assessments.

``In the pilot, set on Air Force One,'' recalls Alexander, ``there was a scene where Kate is sick and Ducky's taking her temperature. The scene was written with her in a chair by a desk, and Gibbs is there. But Don was directing, and as we rehearsed the scene, he asked, 'What would you do?' So I lay down on a couch nearby, and Mark sat on the edge of the couch comfortably, and Don said, 'I kind of like that, let's stay here.'

``We found a tremendous amount of chemistry between Kate and Gibbs,'' she continues. ``There was this moment between two people - Don let it go, and Mark and I found it. We found in Kate a feistiness to stand up to him, and in Gibbs, something he liked about her - soft and vulnerable yet standing her ground. That was a defining moment; those moments let things breathe.''

Weatherly remembers, ``We had to break into this house, and they had written that I threw this rock through the window. I was feeling a little randy and went wild with a little improv. Harmon was a (college) quarterback - he wasn't there that day, but to make the crew laugh, I did this thing: 'He's in the pocket, he's looking downfield - look at the alacrity with which he bounces to and fro!' The next day in dailies, I got in a little trouble for veering from the script, but it worked in the episode, because it became clear that DiNozzo is not dumb but an enthusiastic guy who has some left-of-center ideas about things.''

Weatherly and Alexander have developed an amusingly competitive rapport on the series. ``With Tony and Kate, that's something that just started to happen, because Michael and I just get along really well, and we do have a little brother-sister thing,'' Alexander says. ``You see them and you wonder, 'Are they dating?' They're not, but they're friends. And we enjoyed it so much that I think Don capitalized on it. ... Those kinds of moments make it fun, make it sexy, make it unpredictable. And I love that.''

Bellisario says the cast makes it look easier than it is. ``This show is very difficult to write to my satisfaction,'' he says with a sigh, admitting that shooting begins on episodes before a final script is in place. ``There are only one or two writers who get it. Some can do the forensics, some the story, some the humor, but it's hard to get it all to mesh.''

Harmon is impressed, nonetheless, with how the series has come into its own. ``You can say it's luck, or you can say someone's pretty smart - no question Don's pretty smart,'' he says, adding, ``There's nothing saying that you can take (actors) from different places and put them together and they're gonna get along. I've been on sets where it's hell. It's rare to be on a set where they get it. Here, they get it.''

David Kronke, [phone]

david.kronke(at)dailynews.com

NCIS

What: Military crime-drama with healthy dollops of humor, starring Mark Harmon and David McCallum.

Where: CBS (Channel 2).

When: 8 p.m. Tuesday.

CAPTION(S):

3 photos

Photo:

(1 -- cover -- color) A quiet HIT for CBS

`NCIS grabs viewers with mix of crime, quirky characters and humor

(2) The chemistry and interplay among Sasha Alexander, left, Mark Harmon and Michael Weatherly and the other cast members is a large part of ``NCIS' '' success, say its actors.

(3) no caption (Sasha Alexander with Mark Harmon)