If you know what you think of "Peter Pan" and what you think of Sandy Duncan, you probably have a fair idea what you will think of "Peter Pan" with Sandy Duncan.

There are times in the theater when the whole is something greater - or less, or other - than its parts. This is not one of those times.

So let's consider the parts.

The songs, written by what appears to be a voting majority of ASCAP (to name names, Carolyn Leigh, the late Mark Charlap, Betty Comden, Adolph Green and Jule Styne), include "I've Got to Crow," "Neverland" and "I Won't Grow Up."

The play was written by a single slightly daffy Englishman, Sir James M. Barrie, in 1904. Juvenile delinquency has come a long way since Sir James created his dreamworld of runaway English lads in blissful coexistence with pirates, Indians, fairies and anthropomorphic flora and fauna, but "Peter Pan" has remained a children's theater staple.

It is possible to regard the play, with its neighborly juxtaposition of sense and nonsense and its early venture into audience participation ("If you believe in fairies, clap your hands!") as a daring precursor to today's avant-garde. Silly, but possible.

The current production, which opened a three-week run at the Kennedy Center Opera House last night, is notable for its fanciful array of sets and costumes, its rousing choreography and its mechanical "Flying by Foy." (It may look like wire, but apparently it's Foy.).

And the producers have had the immense good sense to hire George Rose for the dual role of Mr. Darling and Captain Hook, and to dress him up like a peacock for the latter.

Captain Hook's hand, you will recall, was removed by a crocodile who went on to swallow a clock. The Captain holds Peter Pan responsible, and will see him dead for it - although, as Rose blithely admits, "If I were a mother, I'd wish that my children were born with this [indicating his left hook] instead of that [indicating his right hand]."

The centerpiece of the production, of course, is Sandy Duncan of the TV series "Funny Face" and the mini-series "Roots," among her other credits. Duncan sings, dances and flies with authority (as well as with Foy), but somehow she seems to have come off the canned-goods shelf at your neighborhood supermarket.

Every smile, every leap, every gleeful crow is the same. She is, perhaps, simply too well-cast as this androgynous exuberant, eternal youth. Together, the character and the performance are like a candy bar you have inadvertently left in your pocket on a hot day.

This "Peter Pan" runs about two hours and forty-five minutes, which is probably traceable to the fact that the director and choreographer are one and the same Rob Iscove. Iscove the choreographer could have used Somebody-Else the director to tell him to cut a few of his dances, as lively as they are, a bit shorter. As it is, Peter, Wendy and the gang seem occasionally to have gone off to Foreverland instead of Neverland.

But Iscove's dances also provide many of the evening's truly riveting moments, including a simulated underwater dance in Act Three that ends with a willowy ensemble of mermaids gliding gently up into the rafters.

PETER PAN, the play by James M. Barrie, with music by Mark Charlap and Jule Styne, and incidental music by Trude Ritman and Elmer Bernstein, and lyrics by Carolyn Leigh and additional lyrics by Berry Comden and Adolph Green. Directed and choreographed by Rob Iscove; production designed by Peter Wolf; costumes by Bill Hargate; lighting by Thomas Skelton; musical and vocal direction by Jack Lee; and flying by Foy.

With Sandy Duncan, George Rose, Marsha Kramer, Christina Kumi-Kimball, James Cook, Beth Fowler, Todd Porter and Jonathan Ward.

At the Opera House through Aug. 5. CAPTION: Picture, Peter Pan (Sandy Duncan) and friends in flight, by Gerald Martineau.