Ridley Scott's "The Duellists," opening today at the K-B Fine Arts, is a surprisingly effective adaptation of a great Joseph Conrad story, "The Duel," an explosively witty chronicle of a fued that erupts between two young lieutenants in the Grand Army of Napoleon, and endures throughout the period of the Napoleonic Wars because of the implacable belligerence of one of the participants.

An ironic reflection on the bellicosity of Napoleon himself, the story begins in Strasbourg in 1801 when hot-headed, plebian Lt. Feraud takes offense at cool-headed, patrician Lt. D'Hubert, who has been ordered to find him and escort him back to quarters, following a duel in which Feraud killed the relative of a local official.

Presuming himself to be insulted, Feraud turns on D'Hubert and challenges him to a duel. D'Hubert feels reality slipping away - Conrad isolated the moment brilliantly by writing "A profound silence followed this mad declaration; and through the open window Lt. D'Hubert heard the little birds singing sanely in the garden" - but he can't avoid fighting. His antagonist refuses to listen to reason. Only combat and violence will satisfy him.

Feraud is knocked cold in the course of the duel. Still determined to exact satisfaction for an imagined insult, he forces a renewal of the duel at intervals over the next 14 years - whenever there's a breather in the European war. Each time D'Hubert advances in rank and entertains the hope of making further duels impossible, Feraud advances in rank too and insists on another fight. Both men are generals - D'Hubert in the revamped Royalist army and Feraud in cranky, seditious forced retirement - when the dispute is finally resolved.

The movie can't quite duplicate the pleasure that derives from Conrad's cagy, insinuating way of telling this historical parable about human nature at its most perverse and irrational. The meanings remain clear, however, and the filmmaking process allows for other forms of wit and sensuous satisfaction. For example, it seems humorously inspired for Harvey Keitel's Lt. Feraud to turn up looking like that old hothead from Warner Bros. cartoons, Yosemite Sam, during the retreat from Russia. His resemblance to Napoleon in exile in the closing sequences is, of course, even more appropriate, and the resemblance isn't forced.

The true beauty of Scott's direction is that it seems to allow for such spontaneous, witty flourishes within an exceptionally handsome visual framework. "The Duellists" is Scott's first feature, but it reflects a forceful as well as masterly command of settings, lighting and composition. Pictorially, this is the most evocative period movie since "McCabe & Mrs. Miller." It's also the most impressive adaptation of a literary classic since I can't remember what.

Scott studied painting and scenic design before establishing himself as a director with British television series and commercials. He is almost 40 and his log includes over 3,000 commercials, many reputed to be dazzlers. One can believe it.

This movie looks every bit as magnificent as "Barry Lyndon," but the pictorial beauty is more vital and statisfying because Scott never allows his compositions to freeze. The images are frequently splendid enough to take your breath away, but Scott rarely lingers over his setups.

He turns one apparently frozen composition into a sweet jest: Keith Carradine as D'Hubert and Cristina Raines as his wife seem to be caught in a still life, but suddenly she springs to life, and it's revealed that she's been listening intently for signs of life in her pregnant belly. Scott also lingers over a composition at the fadeout, but it's a vision you want to savor, a majestic, wintry early morning shot of Keitel in silhouette overlooking the Dordogne River as the sun slowly emerges beneath an incredible arching cloud formation.

In most respects it would be a blessing if everyone planning a period or costume movie accepted "The Duellists" as a new standard of quality. Scott, however, is left with a few incongruous elements of his own. Attempting to fill out the narrative with a little sexual drama, screenwriter Gerald Vaughan-Hughes gets carried away with one of his inventions, a camp follower played by Diana Quick who becomes D'Hubert's mistress, and allows her an improbable, ineffective confrontation scene with her lover's antagonist.

Keitel and Carradine are vocally incongruous choices for the leads. Keitel, as redolent of Brooklyn as Tony Curtis used to be in period movies, is particularly unassimilated. Carradine doesn't have an instantly disillusioning dialect, but he seems to lack the vocal and theatrical training that would give him command over lines like "I'm not fanatical enough to persevere in this absurdity."

Keitel and Carradine are more than adequate as camera subjects. The latter lloks especially glamorous in hussar gear, and he projects a powerful pantomime of sickened apprehension during the buildup to a duel on horseback. Curiously, two British actors who might have achieved prodigiously witty effects from the roles of Feraud and D'Hubert - Albert Finney and Edward Fox - contribute expert but brief supporting performances, along with a battery of talented compatriots.

The duels were staged by William Hobbs, who performed the same specialty for Richard Lester on his "Three Musketeers" films. As a result, the swordplay looks realistically strenuous and terrifying. You can feel the exertion and the sting of the wounds. Hobbs takes his inspiration from Kurosawa movies rather than Hollywood swashbucklers: His combatants are out to kill. Ridley Scott has made a triumphant directing debut by creating a film that looks beautiful but never loses sight of the capacity for animosity and conflict lurking in the human psyche.