CROSSING NIAGARA by Alonso Alegria; directed by Louis W. Scheeder; set and lighting by Hugh Lester; costumes by Bary Allen Odom; high-wire consultant, Philippe Petit. With Michael Tolaydo and Tobias Haller.

At the Folger Theatre through March 15.

Very early in the course of "Crossing Niagara," the audience realizes it is going to see a man walk a tightrope over Niagara Falls -- with a second man on his back, yet! We have learned in a brief prologue that the real-life hero of this play, the French aerialist Blondin, actually pulled off such a stunt in 1859. This was but one of many crossings, which he would vary by walking blindfolded, going on stilts, turning somersaults, pushing a wheelbarrow, or sitting down halfway across the falls and cooking an omelette.

So neither the survival nor the success of Blondin and his assistant, Carlo, is in question. The question is, rather, how this fantastic feat is going to be depicted on stage, how the magic of theater is going to suspend us on a few inches of rope 165 feet above one of the great natural wonders of the world.

Without giving away the answer, I can report that the high point of "Crossing Niagara" is, unquestionably, the crossing of Niagara. But the other five scenes of Alonso Alegria's two-character play, which opened at the Folger Theatre last night, are so wordy and wearing that this becomes a dubious honor. The spunk of the subject matter is only rarely matched by what Alegria does with it.

We meet Blondin after his 21st crossing, in which he has wowed the multitudes by preparing an eight-egg omelette en route. Alas, he had promised 12 eggs, and among his thousands of spectators, one has noted the discrepancy -- a 108-pound, 18-year-year-old American who calls himself, theatrically, "Carlo." Bursting into Blondin's rooms a few hours after the aerialist's feat, Carlo impudently berates him as a fraud, accuses him of pandering to the masses with "sensational hocus-pocus," and challenges him to attempt something really daring -- like crossing without a rope. If Blondin will train properly, if he will develop his muscles "until each one is as strong and light as a violin string," and if he will practice going faster and faster across the falls, Carlo insists a time will come when the rope itself can be dispensed with. Blondin will learn to walk on air!

Blondin is skeptical, and remains so when Carlo points out, "Birds fly, don't they?"

"They fly," Blondin agrees. "They don't walk on air."

But Carlo's mad enthusiasm keeps nagging at him, so Blondin finally proposes the tandem arrangement, which will require such total coordination between the two men as to necessitate a completely new name for the combined entity -- "Icaron," with apologies to Icarus, the wax-winged mythological bungler who forgot what happens to wax when it gets near something hot (e.g. the sun).

There is rich matter here in the contest (and subsequent collaboration) of a visionary, foolhardy young man and a brave, hard-nosed older man. But it would take some deft dramatic tightroping to balance physics and metaphysics or history and theatrical fancy as Alegria has tried to do. In a program note, the Peruvian-born, U.S.-educated playwright allows that the sum of his original research for "Crossing Niagara" was an article on Blondin in the Encyclopedia Britanica. It shows. The play has little sense of detail or expertise or authenticity, and much of the diaglogue between Blondin and Carlo -- for example, when Carlo asks what falling would be like or why one shouldn't look down -- is disconcertingly naive and general.

As Blondin, Michael Tolaydo gives a smooth, persuasive performance that is long on Gallic gestures and inflections. In his bemused and occasionally baffled looks, we see the confusion and the contained fear of a daredevil embarked on a new dare. But Tobias Haller is mechanically frenetic and consistently irritating as Carlo. Perhaps Carlo himself is that way, but whatever Haller's justification, a two-character play cannot easily suffer so monotonous a fellow.

Although this is its U.S. premiere, "Crossing Niagara" has been produced on several continents and in quite a few languages, demonstrating anew that other cultures have a freer attitude toward theatrical whimsy than we do. Perhaps there is a stimulating cross-cultural leap here for the taking. But this is not a play that seems likely to lure many theatergoers into the breach.