ROCK CONCERTS are to the children of the '60s and '70s what high mass once was to the peasants of Europe. Each event is designed to give rise to a sense of unity that refreshes the society and assures the individual's place in that society. Ecclesiastical rituals provided a comforting feeling of warmth and sameness for the medieval worshipper; in much the same fashion the highly ritualized goings-on at a rock concert give rise to a feeling of togetherness and a solid sense of belonging. The effectiveness of the rock event, of course, is highly dependent on the abilities of the bands involved, and few bands were ever better on stage than the Grateful Dead, now in their 12th year on the musical scene.

But in a rock concert, as in masses, you have to be there to really get anything out of it. Countless concert albums and movies prove that there is no substitute-even in sound or sight-for witnessing the real thing. In any adulterated form, the content usually evaporates, and that is the major problem with The Grateful Dead Movie, which features about two hours of Dead concert footage.

Deadheads all over the world live and die by the foibles of their adopted group, though most rock fans stop short of this sort of idol worship. Still, the Dead are almost universally recognized as a talented, innovative group that is at its best on the stage, rather than in the studio, where most groups hibernate. In some ways, however, the Dead seem stuck in the debris of the late '60s; their music has the raw, unreconstructed sound of earlier groups, and they retain their oft-publicized position as the high priests of acid. Despite the death by excess in everything, particularly alcohol, of the immortal Pigpen (Ron McKernan) back in 1973, the Dead roll on, forever, it seems. Garcia (Captain Trips himself and the director of the movie), Lesh, Weir, kreutzman and Hart have played together for so long that they have developed the kind of tightness few groups can ever hope to achieve.

The movie, however, has some problems, most of which involve the loss of that vital energy generated in a concert hall where everyone else is high along with you. Instead, you see the Dead in a movie theater, and somehow the feeling just doesn't communicate that well. The footage itself is excellent, featuring good camera work and more shots of Jerry Garcia's grungy fingernails than you ever thought possible. In many ways it is stock rock film stuff-pans of the audience cutting to tightly focused shots of Garcia's hirsute mug or Phil Lesh's rather spaced-out expression; then a cut to somebody's fingers working magic on a guitar.

Those who find inner peace listening to Dead music will rush away on this film, for it features the group at its performing best. Rumor has it that the Dead have never given a poor performance, and this film seems to legitimate that claim. Some of the best tunes--"Sugar Magnolia," "Playin' in the Band," "U.S. Blues," and the immortal "One More Saturday Night," are included in the film.

ACTUALLY, the best part of the film has very little to do with the Dead themselves. The opening sequence features some gimmicky, funky animation, including a wild sequence of what can only be characterized as cosmic pinball. Also involved in the animated sequence, which runs about five minutes, is the skeleton character featured on several Dead albums.

Another surprisingly good part of The Grateful Dead Movie is the attention paid to the audience. Most rock films throw in a shot of some wildly-shrieking pretty young thing in the front row to break up the action a little bit, but this movie has an unusual-and unusually good number of audience shots. Pretty girls abound, of course, including two rather stoned out young women in obscene costume, but the focus is really on the Deadheads themselves. The Deadheads constitute the most devoted fans in the rock world since the Beatles stopped touring back in 1966, and they are a singularly fried bunch of people. Their enthusiasm, expressed in their LSD-induced nodding stares, is captured in harmony with the music they flock to hear.

A reaction to The Grateful Dead Movie must ultimately depend on one's opinion of the Dead themselves. Deadheads all over the United States will love this film and see it as many times as they can, preferably while: a) stoned out, or b) tripping. For a non-rock enthusiast, forget it, and for the average rock fan, well, this is just a very average rock movie, and on the long side at that.