A Prayer for Owen Meany, National Theatre Lyttelton, London

A good God is hard to find

"I am doomed to remember a boy with a wrecked voice..." declares John Wheelwright, the narrator figure whose troubled memories take to the stage in A Prayer for Owen Meany. That voice would certainly haunt anyone. High-pitched, squeaky and nasal, it makes Bugs Bunny sound like Paul Robeson. Its owner is the eponymous hero, a bizarre dwarf of a boy who is also, it seems, a prophet.

At the age of 11, while playing in a Little League baseball game, Owen hits a foul ball that kills the mother of his best friend, John. He becomes convinced that he is God's instrument, and subsequent dreams and visions foretell the time and manner, but not the place, of his martyr's death. His life, which becomes embroiled in the Vietnam War, is a preparation for that moment. In his opening speech, John reveals: "I am a Christian because of Owen Meany".

Watching Simon Bent's adroitly filleted stage adaptation of the prolix cult novel by John Irving, I kept thinking of a speech from a comedy by John Guare. "I don't know much about symbols," avers the character, "but I'd say that when frozen flamingos fall out of the sky, good times are not in store."

Portentous pointers with this absurd degree of coercion compel us to perceive Owen as no ordinary child. When a boy volunteers to be both Jesus in a nativity pageant and the Ghost of Christmas Yet To Come in a play of A Christmas Carol, as Owen does, he's evidently not thinking small about his role in the great scheme of things.

The book and play are at pains to establish that our hero is far from being a model of conventional piety. Aidan McArdle's vivid Owen is a goofy, bucktoothed sprite with a droll line in snappy subversion. There's even a sequence where, with a merciful drop in vocal register, his dissenting views on US foreign policy are presented as a Lenny Bruce-style stand-up routine. Why, then, is this figure prepared to submit himself to the will of a tyrannical God who, in his eyes, has used him as a murder weapon, and insulted his mother with the imposition of a virgin birth?

The piece purports to be about the difficulty of belief in a world where there is no obvious evidence for the existence of a deity. What you get, though, is not a genuine examination of belief, but propaganda for it. The drama would be stronger if there were a radical ambiguity in interpreting Owen's life as testimony to a divine plan. The overriding impression here, however, is that it was an objective miracle and that Richard Hope's John – too often left looking slightly de trop as the agonised observer of his past – was simply tardy in acknowledging it as such.

A movie version, entitled Simon Birch, apparently reduced the piece to a schmaltz-fest, and Irving has argued that the novel is unfilmable because, in that two-dimensional medium, "to visualise Owen's miracle is to make it unbelievable". Mick Gordon's spare, witty, almost abstract staging in this Lyttelton production suggests that – even when you cleverly draw on theatre's capacity for emblematic short-hand and for telling dream-like mergers and juxtapositions – the story of Wonder Boy, when put to the test of dramatic embodiment, still comes across as sentimental fantasy. The clarity and concision of the adaptation are admirable, but this is not a conversion job that is going to win many converts. "On Faith" is its advertising slogan. That should be changed to "On Wish-fulfilment".

To 29 June (020-7452 3000)