"Rockers," an epic of reggae life in Jamaica opening today at the Inner Circle, is a small movie with a great heart.Like "The Harder They Come," which in 1973 introduced American moviegoers to the Rastafarian intrigues of the same record-crazy Caribbean island, "Rockers" pulsates with an offbeat joy of life.

The difference is that Jimmy Cliff, the rheumy-eyed charismatic of "The Harder They Come," was fated to become a tragic outlaw and folk hero. "Rockers" offers a different kind of leading man: the gangling, dreadlocked Leroy "Horsemouth" Wallace, a sweetly-disposed reggae drummer whose revenge against the forces of Establishment "Babylon" is anything but sour.

"Rockers" -- the word is another term for reggae, the elusively syncopated popular music of Jamaica -- has an unlikely history. It was shot in eight weeks in 1977 on location by Theodoros Bafaloukos, a Greek-born graduate of the Rhode Island School of Design who discovered reggae during a trip to Kingston in 1975. He then set out to make a film which would portray the reggae musicians of Jamaica "as they saw themselves."

Bafaloukas chose real musicians to tell their own story, and the story they tell is that of hard-pressed but highspirited culture seen from the inside. Though "Rockers" has its documentary aspects, it is no National Geographic article; the bouncy plot in which Rastamen and their adversaries fight hammer and tong in a world where whites, when they appear at all, are mere ants at the picnic.

Horsemouth himself exudes star quality of the first magnitude, immediately emerging as a man of action unburdened by cause-and-effect sociological fate. This hero is no more misunderstood than a bottle of Dr. Pepper. That doesn't go for his language, however: Most viewers will be unable to understand a word he or any of his companions says, since they speak in a Rasta patois which revelas its meaning only through constantly entertaining subtitles.

Horsemouth's story is this: Despite a reputation as "the hardest drummer" on the island, he must support himself by selling records from a rack on his motorbike. The bike, with its gas tank emblazoned with the Rastafarian Lion of Judah, is an icon in the manner of the guitar in Black Orpheus.

Horsemouth's troubles begin when he takes a job with a band in a nearby town and dares turn his attention to the beautiful Sunshine Marshall, whose birthright is middle-class and whose father is Mr. Marshall, a corrupt club owner. Mr. Marshall, like everybody else of social standing on the island does not cotton to the dreadlocked Rastamen, with their impenetrable dialect and marijuana-soaked ways. He is Vanity Fair, a member of the Babylon which constantly assails the Rasta world. Pretty soon Horsemouth's philosophy is sorely tested, his motorycle is stolen ("Rasta! Them thief I-man bike!") and he is beaten up.

His attempts to regain possession of the Lion of Judah gives the film ample room for a picaresque tour of Jamaican life, which seems populated exclusively with musical groups hot on the local charts (Kingston artists turn out 45 new 45-rpm records weekly). Horsey visits with Winston Rodney, the reggae singer known as Burning Spear; he consorts with the Mighty Diamonds, a reggae group which operates a metal shop when not performing, and so on. The leader of the Diamonds, looking up from his acetylenetorch to assent to Horsemouth's plan of vengeance, sounds a typically pretty note of dialogue: "The most that I can show thee-I, Horsey, is love."

Nearly everybody plays himself here. Horsey's wife, who calls him Leroy, is his real wife, and her nagging seems quite unrehearsed. A droopy-lidded hilltop holy man is played by Ashley "Higher" Harris, whose previous credit is that he has spent the past 14 years living high over Montego Bay, growing wise and hairy. (Rastafarians do not cut their hair; the resulting mass is known as dreadlocks.)

By the time the plot has thickened, it is clear that gentle Horsey has a clever sense of vengeance. This is fully proved by the way in which the corrupt Mr. Marshall -- whose beautiful daughter has sided with Horsemouth -- gets his just desserts.

The Rastafarianism with which "Rockers" is imbued originated with Marcus Garvey in the 1920s. Its members believe that Ethiopia is the promised land of Zion and that Ras Tafari Makkonen, who was crowned Emperor Haile Selassie in 1930, is the Messiah. The sect renounces Christianity as a slave religion, and with it mercantile society -- known collectively as Babylon. Reggae is the means of Rastafarian self-expression, which also makes itself manifest in the smoking of ganja (marijuana), the wearing of dreadlocks and a disinclination to work for wages. This is fairly antisocial stuff in Jamaica, where Rastament and police are continually at odds.

But nothing the Rastamen do to vex Babylon works more effectively than their exclusionary language. In Rastatalk, the first-person never appears in the objective case, always in the nominative, and frequently hyphenated with "man." That goes also for plural constructions such as you and me. What Horsemouth says to Burning spear, inviting him to the water's edge for a chat, is "I and I will step down to the beach."

Thus Horsemouth, seeking admiration for his motorcycle, asks: "The man love I-man transport?" Appearing before his brother dreads with a battle plan, he informs them: "I-man want thee-I to go upon a business." Annoyed when his friends fail to take him seriously, he exclaims: "I-man vex, Rasta. What joke to you, me dead, man." It takes some close following, but there is apparantly also a Rastapun, as when two companions await Horsey, unaware that he is at that moment taking a licking:

Q. The man sight Horsemouth?

A. No, mahn.Horsemouth are a late brother.

The Rasta patois, in fact, attains heights of poetry when made to carry issues of pride. After Horsey is pummelled by a Babylonian, he raises up and turns to the camera, a glowing combination of Falstaff and the New Testament, to say:

"I and I don't deal with violence. I and I is peaceful Rasta man. No matter what the weak heart say, I and I is like a tree plant by the river of water. Not even the dog which p -- against the wall of Babylon shall escape this judgment. All of the youth shall witness the day that Babylon shall fall."

More remarkable even than the language is the fact that "Rockers" was made at all. It treads light-heartedly over the same terrain as "The Harder They Come," without ever apologizing. It is filled with music but -- in an amazing lack of deference to commercial possibilities -- lacks a main title song. And it manages, using entirely indigenous amateur actors, to go 99 minutes without ever slowing down or making a wrong turn.

"Rockers" is not a case of life imitating art, nor of art imitating life. Maybe it's just art imitating art. Whatever it is, it's wonderful.