CROSSING NIAGARA -- At the Folger through March 15.

"Crossing Niagara" at the Folger is the best magic act in town.What happens is, every night Michael Tolaydo and Tobias Haller get up on the stage and, right there in front of God and everybody, they make an omelette out of bricks.

"Niagara" is the first U.S. production of a drama about Blondin, the 19th-century aerialist who made fame and fortune commuting between the U.S. and Canada via tightrope above the falls, and a young fan who won't get off Blondin's back until the Frenchman carries him across.

It was written by Peruvian playwright Alonso Alegria, who also translated it into heavy and sometimes stilted English, which adds to the burden of symbolism the actors must carry.

Instead of trying to play around their occasionally almost unspeakable lines, Tolaydo and Haller charge right on through with wit, humor, power and craft, and so manage to keep all the verbiage from obscuring the idea. They are in such firm command that the lines don't dare clunk.

What Algeria's pen can create when held in check is shown in the scene where Blondin and Carlo are revealed to be psychic if not actual orphans. It is the pivotal step in the development of his characters, and instead of hammering it home he lets it fall and then lets it go.

Tolaydo as Blondin and Haller as Carlo keep the tension of the piece in nearly perfect balance throughout, successively or simultaneously representing age and youth, strength and weakness, art and science, experience and purity, wisdom and enthusiasm, father and son and, ultimately, the banishment of shared loneliness and fear by trust and interdependence.

But "Niagara" doesn't play like that. It plays like what might have happened if a brash but engaging boy had badgered Blondin into carrying him across the falls on an 1,100-foot rope 160 feet above the water. Both characters, and the situation, are so believable that in the final act the audience unconsciously leans and strains, trying with body English to keep the teetering man and boy from falling into the abyss.

It's a marvel, that last act, in both staging and performance. Designer John Hodges has supported the players' straightforward performance with a simple setting that lets the viewer's mind suggest the windy void. One comes to believe that a false step could send both men tumbling into space.