BILL IRWIN has made a fine art of fooling around. And Irwin's irresistible "The Regard of Flight" at Arena's Kreeger Theater, too short at an hour and a quarter, engages the brain along with the funny bone.

Though he performs with no makeup but his boyish grin, "new vaudevillian" Irwin is the quintessential clown, a sweet-natured master of pratfalls and funny faces.

But this stuff is not just nonsense -- "Flight" is also a good-natured nose-thumbing at Postmodern Theater.

Irwin's nightshirted alter ego has fallen asleep reading "Toward a New Theater," and finds himself trapped in a recurrent actor's nightmare: waking up on stage, being sent -- always unprepared -- through his frantic paces by a demanding director/pianist, played with delicious deadpan by Douglas Skinner.

As Irwin performs, switching swiftly from abject terror to comic bravado, he lets us all in on the theater's "in jokes," simultaneously spoofing and celebrating the "new theater," with its pompous manifestos, its mistrust of and reliance on old styles and its tendency to have all its "devices" showing ("to demystify the theatrical experience").

Skinner frequently interrupts the proceedings to dryly deconstruct Irwin's "contemporary performance piece," dropping highfalutin buzzwords like "formalist construct" with a straight face.

Can it be coincidence that Irwin comes to town just as we're visited by other troupes proclaiming their search for new forms? In fact, "Flight" may be the perfect companion piece to Peter Sellars' "A Seagull," which attempts nearly all the things Irwin merrily sends up.

Irwin also refreshingly knocks longwinded theater critics down a few pegs -- he even impales one, vampire-like, with his own oversized pencil. M.C. O'Connor plays the hyperaggressive critic who badgers poor Irwin to the point of chasing him through the aisles.

The evening ends all too soon with a charming series of brief "Clown Bagatelles," a virtuoso survey of more traditional clowning.

The endlessly inventive Irwin was recently awarded a MacArthur Fellowship for his comic genius -- maybe he'll use the money to build his own "new theater" so we can see him more often.