KAPLAN'S DOCTOR IS JUST WHAT THIS PLAY ORDERED.

Byline: Julio Martinez Special to the Daily News

The Corelli family will never be mistaken for the Sopranos or the Corleones, but that doesn't mean they don't have murderous ambitions. They're just extremely inept at it.

``Thicker Than Water,'' Roy Batocchio's comedic look at a New York-based Italian family that plots to eliminate a meddlesome in-law, never quite achieves the necessary comedic flow, but it does have its moments. Director Stu Berg conducts the proceedings at too deliberate a pace, seldom allowing Batocchio's plethora of clever sitcom antics to ignite.

The production is more than worth the price of admission, however, if only to witness the flat-out hilarious portrayal of the family physician, Dr. Flanken, by veteran sitcom actor Marvin Kaplan (``Alice''). Batocchio, who wrote for TV's ``Love Boat,'' has layered the plot with comical malevolence. L.A.-based television writer Tommy Corelli (Dave Scotti) has been hurriedly summoned back to the family home in New York by older brother Carmine (Roger Cruz) to help in a family crisis.

Tommy immediately becomes a confidante to everyone's supposedly secret plot to do away with Uncle Albert's (Jack Kutcher) wife, Gertrude (Susan Morgenstern), a childless, dominating shrew who has decided to use her money and political influence to take over the Corelli construction business.

Carmine and sister Marie (Cecily Adams) have hired a hit man. Tommy's dad Dominick (Leonard Ross) and Albert have hired kidnappers. Mama Rose (Constance Mellors) has arranged to have cellar-dwelling Grandma (unseen) shoot Gertrude when she comes over to visit. And even Carmine's mild-mannered but emotionally volatile girlfriend, Meredith (Barbara Mallory), could turn murderous (she carries a pistol) if provoked.

The ensemble fails to adequately spotlight the playwright's obvious punch lines, seldom achieving the energetic rapport and zaniness necessary to convey the farcical ineptitude of the family's efforts to do in Gertrude. Scotti exudes the correct level of incredulousness as Tommy, and Morgenstern is properly flamboyant as Gertrude.

Also scoring points is Mallory's quirky portrayal of Meredith. But Adams, Cruz, Kutcher, Mellors and Ross are often understated to the point of appearing malnourished. However, when he's on stage, Kaplan's Dr. Flanken takes the production to another level. He doesn't play farce - he is farce.

Tom Giamario's well-lived-in design of the Corelli household does much to lend authenticity to the proceedings, as does sound designer Joe Morrisey's mood-setting use of Louis Prima recordings.

The facts

--What: ``Thicker Than Water.''

--Where: Theatre West, 3333 Cahuenga Blvd. W., Los Angeles. [phone].

--When: 8 p.m. Thursday through Saturday, 3 and 7 p.m. Sunday; through Feb. 27.

--Tickets: $12.

--Our rating: Two and one half stars

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Photo: Leonard Ross, left, Jack Kutcher and Cecily Adams are part of an inept Mafia family in ``Thicker Than Water.'