"Fun is Number One."

That's the cheerful motto of the two teenage girls who are the focus of "Fun," an ironic title for this stark shocker, which boasts a pair of knockout performances but loses impetus when its quirky, unfocused narrative begins to unravel.

In its way, "Fun" resembles "Heavenly Creatures," which was also about two young girls who bonded to the point of obsession and then committed a heinous crime together.

But in "Fun," grandstanding is the thing, as director Rafael Zelinsky overplays his use of showy technique to a distracting degree.

The story, by James Bosley (based on his own play), has a pair of lonely, attention-starved Los Angeles teens, Hillary (Renee Hum-phrey) and Bonnie (Alicia Witt), meeting on the morning of a very long day. They hit it off immediately, though it becomes apparent that much of what they have to say about themselves is fabrication.

Both are deeply troubled, but Hillary's actions seem more calculated, while hyper Bonnie has obviously lost touch with reality, constantly bouncing off the walls, her long red scraggly hair flying every which way.

After spending most of the day together, filled with activity that kindles a friendship transcending anything they've experienced previously, the two go into the suburbs, and together they kill a little old lady.

Why? Just for fun . . . or so they tell their interrogators.

The interview process, as the girls talk to reporters and social workers, is the film's framing device, filmed in grainy black-and-white with off-kilter, hand-held camera angles. The events of their meeting, activities and the murder are shown in flashbacks, filmed in sharp, striking color.

This back-and-forth device wears out its welcome rather quickly, however, and some of the dialogue seems to go on forever without much point. The biggest drawback, however, is the film's lack of insight into its two central characters.

As an acting exercise, however, it's quite startling, and the performances by Renne Humphrey and Alicia Witt are remarkable. (Both won a special acting award for this picture at the Sundance Film Festival in 1994.)

"Fun" is not rated but would probably receive an R for violence and language.