"A Bridge Too Far," opening today at seven area theaters, is an unusually conscientious and impressive war epic. Produced by the inimitable Joseph E. Levine and directed by Richard Attenborough at a cost of about $25 million, the film at least justifies the expenditure in terms of careful period recreation, visual spectacle (the sequences depicting paratroop landings are particularly awesome), the mixture of exciting combat episodes with vivid human interest vignettes, an effort to establish a coherent, many-faceted view of a complicated and ill-fated military adventure, and a generally superior level of film-making intelligence and craftsmanship.

As big war movies go, this one belongs at the head of the class with attractions like "Patton" and "Lawrence of Arabia." While "Bridge" has its failings - and I think there's a most unfortunate failure to resolve the story emotionally at the fadeout - it never sinks to the level of a "Tora! Tora! Tora!" or "Midway." When it falls short, it does so without insulting your intelligence or losing your respect.

Even the levine gambit of rationalizling a steep budget by hiring several stars at salaries that jacked the budget even higher - Robert Redford, at $2 million, was the prize catch - has paid better dividends on the screen than one might have expected. The star presences in "Bridge" seem less obtrusive and disillusioning than their counterparts in "The Longest Day," Darryl F. Zanuck's reproduction of an earlier best-seller by the late Cornelius Ryan, who had a remarkable literary knack for reconstructing battles in a vast yet invariably lucid and dramatic mosaic form.

Ryan O'Neal and Liv Ullmann are the only downright unsatisfactory performers in "Bridge>" which deals with an unsuccessful Allied offensive called Operation Market Garden, an attempt to establish a bridgehead across the Lower Rhine by landing 35,000 airborne troops (two American divisions, one British division and a Polish brigade) behine German lines in Holland in September of 1944. O'Neal's inconcealable callowness stems a dreadful disservice to a military man as gallant and thoughful as Gen. James Gavin, who commanded the 82s Airborne Division. O'Neal is the only leading actor in the cast who defies credibility as a man who has seen combat and could lead other men in battle.

Redford evidently had his choice of roles, and one can understand why he might have preferred to appear as Julian Cook, a major in the 82nd who led a battalion on the single most daring attack in the American sector of the battle, a river corssing that succeeded in capturing the north end of the bridge at Nijmegen, the division's ultimate objective. Nevertheless, I wish Levine had urged Redford to portray Gavin, because it might have kept his stellar chain of command in perfect balance.

The sight of Ryan O'Neal giving orders to Robert Redford offends one's sense of the rightness of things. Not that O'Neal would possess any more authority pretneding to otder aournd Dirk Bogarde, James Caan (who plays a sergeant), Michael Caine, Sean Connery, the astonishing Edward Fox (who does a brilliant turn as British armored commander Gen. Brian Horrocks), Elliott Gould, Gene Hackman (a fine, fierce Polish general) or Anthony Hopkins, whose custmary neurotic creepiness has totally vanished in the role of Lt. Col. John Frost, the British paratrooper whose battalion reached the ultimate objective of Market Garden, the bridge at Arnhem, and held out for a week under pulverizing German counterattacks.

An incidental effect of the casting is to separate the actors who can impersonate commanding personaliities (of several temperaments and nationalities) from those who can't.An unfamiliar actor named Paul Maxwell does a more convincing job as Gen. Maxwell Taylor, who commanded the 101st Airborne Division, than O'Neal has as Gavin.

Hopkins isn't the only performer to improve under Attenborough's direction. Arthur Hill, oftern a bore on the screen, is excellent as an Army surgeon in a taut, fiscinating episode centering on Caan's character. Maximilian Schell, usually to be avoided when he dons a German uniform, proves a restrained, elegant Gen. Bittrich.

The Ullman case is a bit mysterious. She ought ot be ideal as Kate Ter Horst, a Dutch housewife whose home was turned into a hospital for wounded paratroopers. Form some reason the filmmkaers fail to show her actively engaged in nursing the wounded, an obligation her prototype certainly assumed. Ullmann seems to drift about bestowing voice - over benedictions on dying soldiers, and the effect is ludicrously condescending. It's as if she were only a movie star passing through.

The ringer in the cast is Fox, who probably drew the smallest salary of the 12 official "stars." He played the lead in "The Day of the Jackal," and while that was an intriguing performance, it contained no hint of the charismatic charm he brings to the portrayal of Gen. Horrocks. As far as I'm concerned, Fox should be given all the year's supporting actor awards by acclamation right now. This is the kind of rousing, delightful performance that seems to jump off the screen without jumping out of character. After hearing Fox brief and encourage his men, you feel ready to follow this particular man to the ends of the earth.

Market Garden was designed by Field Marshal Montgomery to out-flank the retreating Germans and end the war in Europe by Christmas of 1944. The speed of the Allied advance since the D'Day landings evidently helped create an attitude of over-confidence that undermined Market Garden. German resistance was grossly underestimated. The British 1st Airborne Division, assigned the Arnhem Bridge, suffered almost 80 per cent casualties, and the entire operation incurred twice as many Allied casualties as D-Day.

Cornelius Ryan drew the title from a remark made by Lt. Gen Frederick Browning, deputy commander of the First Allied Airborne Army, at a final conference at Montgomery's headquarters a week before the operation began.Airborne troops were supposed to seize a large number of river and canal crossings from the Dutch-Belgian border to Arnhem, 64 miles to the north. Horrock's XXX Corps of armor and infantry were supposed to speed to their relief, along what turned out to be a treacherous, more or less one-lane highway. Montgomery assured Browning the armored column could reach Arnhem in two days. Browning said, "We can hold it for four, but sir, I think we might be going a bridge too far." It was a prophetic remark.

William Goldman's screenplay is an intelligent condensation of the book. Goldman tries to retain a comprehensive view of the operation while sketching in as many personalities and episodes as time permits. Goldman is very adroit at writing obligatory expository lines that fill us in without becoming a pedantic burden. In general the script seems structurally sound and subtly effective.

Nevertheless, there's something missing in the last analysis. "Bridge" is a stirring succession of episodes, but the episodes don't quite add up to a movie with a unified, powerful vision. It's not as if the filmmakers have done something wrong. They seem to have left something out, perhaps an explicit closing statement that might sum up the complex of feelings aroused by witnessing an epic about an ambiguous military operation, a calculated risk that didn't quite pay off.

Attenborough tries two possible endings without completing the emotional intent of either. Ryan used ironically contrasted quotes at the end of the book that might have rescued the film from its curiously flat signoff. In the first, Montgomery insisted that the operation "would have succeeded" given a few breaks here and there, and it might have. The second quote came from Prince Bernhard of The Netherlands: "My country can never again afford the luxury of another Montgomery success."

Although the film closes with images of refugees, it might help American audiences in particular to hear an explicit comment on what the failure of Market Garden cost Dutch civilians in the unliberated parts of the country. Moments earlier, Attenborough shies away from a heartfelt coda, a scene of wounded and battle-weary paratroopers singing "Abide With me." One doesn't feel it would be mawkish to stay with these soldiers for the song's completion, in part because one has grown to trust Attenborough as an action director of both uncommon vigor and discretion.

There's an element of reserve in Attenborough - and Goldman too - that can result in missed opportunities. At the end one waits for a resolving chord - orepilogue - that never comes.

Most of the hitches occur in the closing stages of the film. The filmmakers somehow lose track of Frost's beseiged men at Arnhem as the primary focus of suspense, the gallant last outpost. The scenes of the withdrawal from Arnhem are ragged and confusing. Browing's "bridge too far" remark is dropped in after the defeat, making it sound uncaring rather than prophetic.

The production work is exceptional, especially Geoffrey Unsworth's cinematography, which sets a sensitive, expectant viewpoint from the opening shot and often makes scores of tanks and planes seem like thousands. One may feel limitations on the dramatic side, but "Bridge" is an unqualified pictorial achievement.