Any newspaper reporter who is not terminally smug or incurably foolish is bound to recognize in due course that he is not up to his job. That failure has less to do with character than with circumstance. He is condemned to search for the truth through a glass so darkened and distorted that he cannot safely tell but only guess at what lies on the other side.

However earnestly we may go on contending with the handicaps that encumber us, reporters learn to live with and be resigned to them most of the time.

But every now and then something comes along crushingly to remind us that daily journalism cannot escape being only a shadow of actuality; and then resignation turns to despair.

John Castelucci's "The Big Dance" is just such an event. Dodd-Mead does not expect to publish it until next April; but the galleys are going about and the lessons they have to teach are striking enough to excuse such discourtesy as may lie in not putting off comment upon them until spring. Work of high merit gets noticed so seldom that it cannot be noticed too early.

Castelucci's subject is the October 1981 robbery of a Brink's armored truck in Nanuet, N.Y. Two policemen and a security guard were killed in a crime executed with an incompetence that may to some extent account for its savagery. The most dangerous bandits are those who cannot keep their heads.

Thirteen persons are in prison for acts either directly or tangentially connected with the Nanuet murders. One was killed by the police a day later; and the director of the enterprise is the only one still at large. The case has been disposed of; and yet we had to wait for Castelucci to begin to understand an affair that no journalist, no juror, no witness and not even a public prosecutor had before managed to make coherent.

Every horror becomes a routine affair only too soon; and it is unlikely that the Nanuet robbery would have held public attention long if it had not been for Kathy Boudin.

Kathy Boudin is the white graduate of Bryn Mawr College, caught in the U-Haul truck that was the escape vehicle for a black action squad. Castelucci makes it clear that her part in the play was tangential; she was useful as protective coloration for the real soldiers; they were black and from the street; she was white and from the middle class. When policemen on the chase for violent black criminals confront a van driven by two mild-seeming, young white people, they do not easily suspect it of transporting dangerous cargo.

Kathy Boudin looked like someone with whom respectable society identifies. She might have been our daughter gone wrong; the other players on the scene, including ironically the victim policemen, were from a class below hers and definably strangers. We who are licensed to report and comment have at least a fingertip's grip on some social status; and, when deviant conduct strikes our interest, it is generally the deviance of people like ourselves.

Kathy Boudin constitutes most all of the command on surviving memory of Nanuet- Brink's; and yet, like the other white components of the venture, she was only a quartermaster; the combat troops were the blacks, who have learned again that even when you try to shoot your way into history, one of your social betters will still get most of the ink.

From paying too much attention to the supernumeraries, we overlooked the soloists. The white auxiliaries are enduring prison terms that, while not undeserved, relieve them of further stricture; but in Castelucci's account they come off poorly; they were, he surmises, mostly shipwrecks from the radical '60s who turned to an alliance with black troopers who would pull the triggers from which their own fingers flinched.

The true soldiers interest Castelucci more, and he makes them creatures of authentic fascination. Each emerges in an intricacy of strength and weakness. Their original motive for entering upon armed robberies was at least in part to raise funds for the community of the black poor.

In time, their two best soldiers recoiled after their first murder and dropped out; and Kathy Boudin and the others of her class got their first chance for active comradeship with these black revolutionaries at a juncture when their leader planned a glorious attentat for cash to support his cocaine habit and rejoiced at having acquired a combat lieutenant who was out to salvage his bankrupt call girl stable.

Castelucci is the first observer to care enough about the main actors in this story to bring them to a foreground where they loom all at once to shock, appall and in some way impress us with their horrid force. They are the real thing, and Castelucci is the first to see it. Our class had rendered us half-blind, and it seems somehow a miracle to come now upon one of us who wasn't.