AMONG ITS other legacies to American popular culture, "Star Wars" has bestowed the benediction. "May the Force be with you." As a theological concept or mystical source of spiritual strength, this particular Force interests me not at all. However, the imaginative force behind the Force - filmmaker George Lucas - seems to loom even large as one contemplates the immediate prospects for American movies.

Two recent openings, the revival of Lucas' sublime nostalgic comedy "American Graffiti" and the premiere of producer Allan Carr's slimy film version of "Grease," have combined to reinforce my feeling that Lucas is the force that matters. Not the whole force by means, but the most influential and strategically important young filmmaker now operating within the mass audience marketplace still dominated by Hollywood.

At the very least I think it's resonable to regard Lucas, 34, as the senior Good Guy in a Dynamic Duo whose slightly junior partner is Steven Spielberg, 30. Close friends, they may also be responsible for much of the prosperity that has returned to the American film industry.

Spielberg's "Jaws," the great popular hit of three summers ago, rapidly supplanted "The Godfather" as the modern boxoffice champion. Lucas' "Star Wars," the great popular hit of last summer, took longer to overtake "Jaws," but there was little doubt that it would. By the end of the year "Star Wars," and "Jaws" ranked 1-2 in Variety's all-time hit parade, with film rentals of $127 million and $121 million, respectively.

Their success has probably created a climate of enthusiasm and anticipation that will make it easier for the next popular movie of comparable quality and impact to catapult to the hope of the Variety chart. Even blatant imitations can grown to be box-office giants in this climate, as the capacity turnouts for "Jaws 2" in its first weekend of release indicate.

The ideal arrangements for the movie business would be the release of a new Lucas or Spielberg adventure spectacle every summer. However, it seems safe enough to bank on inferior merchandise, especially if certain merchandising techniques are perfected. For example, whoever put together the trailers for "Grease" and "Capricorn One" appear to posses more cinematic style than the folks who assembled the finished products. The same thing was true of "Silver Streak" a couple of years ago.

The danger is that popular filmmaker who also respect the audience and have some artistry in their souls, like Lucas and Spielberg, may ultimately be undermined by a mass audience perceived to be susceptible to everything, the shamelessly despired and transporting pop.

Nevertheless, if the liveliest traditions of American popular filmmaking are going to be renewed and sustained, the creative impetus is going to come from talents like Lucas and Spielberg, not from producers as tasteless as Allan Carr or Lord Lew Grade, the eminence gauche behind "Capricorn One."

Spielberg now has a second box-office titan to his credit, "Close Encounters of the Third Kind," Lucas already had "American Graffiti," which stands in 13th place in the Variety list with rentals of $47 million. When the figures are updated after the summer's revival, the total should be close to $70 million. In all likelihood "Close Encounters" and "American Graffiti" will be among the Top 10 when Variety publishes its next annual accounting. "Star Wars" confirmed the assurance and decency of the popular instincts that Lucas demonstrated initially in "American Graffiti," just as "Close Encounters" confirmed the agreeable flair that Spielberg brought to "Jaws." It must have been apparent to astute people in the movie business that these directors had extraordinary promise even when their first features, "THX-1138" and "The Sugarland Express," failed at the box-office.

Their examples illustrate the importance of keeping faith in abudant, self-evident talent. Similar possibilities are apparent now in first features like Robert Zenneckis' "I Wanna Hold Your Hand" and Martin Brest's "Hot Tomorrows" or an undeserving flop like Jonathan Demme's "Citizens Band." In the long run the initial box-office returns on these movies will be immaterial. The important thingis that the filmmakers keep working at the projects they care about.Sooner or later - and in today's market it's usually sooner - they will prove sound commerical as well as artistic bets.

"American Graffiti" serves as a reminder of how satisfying and far-reaching the eventual breakthrough can be. The movie was rejected at least once by every major distributor. Universal finally bankrolled it on a measly $780,000 when Francies Ford Coppola, flush from "The Godfather" and eager to help his protege Lucas, agreed to form as producer, a subtefuge that left the working producer, Gary Kurtz, with a euphenmistic title of "co-producer." The film's success fueled the careers of several promising newcomers and relative unknowns, from leeading player Richard Dreyfuss to bit player Suzanne Somers.

Reseeing "Graffiti" in the wake of "Star Wars" may also help to clarify the nature of Lucas' power as a popular movie artist. It appears to originate in the representative emotional quality of his experience as a small-town American boy. At once mechanic and dreamer, a combination recalling Edison and Disney, Lucas seems to have acquired considerable mechanical aptitude while partaking of widely shared generational behavior patterns, friendships and romantic fantasies.

He's not a parochial small-towner. Despite the savory nostalgic atmosphere, Lucas perceives the tensions and limitations implicit in the setting and period. It's a tender recollection but never a mawkish or starry-eyed one. Like the homesick but still outward-bound Curt, played by Dreyfuss, Lucas has ambitions and imaginative inclinations that require a more expansive universe.

In "Star Wars" the setting expands to outer space, but one always feels right at home. The fantastic space hardware itself is dented, soiled and scratched to convey the impression of prolonged use. The machines invariably show signs of wear and tear. Looking through the futuristic designs, one can perceive the hot rods and pieces of machinery that must have littered the garage when George was a teen-age drag racer. Emotionally, it's all very familiar and reflects a secure, reassuring value system. At the same time Lucas possesses a command of movie graphics and storytelling that enables him to modernize and revitalize banal settings and longings.

"Graffiti" and "Grease" might be used as textbook examples of adroit and maladroit craftmanship in a variety of categories - period recreation, characterization, dialogue, romance, pop music influences, lyric sensibility. It would prove especially edifying to compare set pieces, like the staging and shooting of the high-school dance in "Graffiti" with the staging and shooting of its counterpart in "Grease," in order to illustrate the gulf between stylistic sophistication and desperate barbarity. Although not a musical in the strict sense, "Graffiti" is essentially more of a musical than "Grease," whose essence is graceless and anti-romantic.

Lucas seems to inspire a unique respect within the business. Even people who criticize him as a "popularizer" do it with a tone of respect. There's never a hint that his popularizing tendencies are cynical or inauthentic. If he's a popularizer, he's a real one, a popularizer with a touch of genius.

In a recent interview director Michael Ritchie, who lives near Lucas in San Anselmo, Calif., mentioned his younger colleague in a revealing way. Ritchie was praising the management of United Artists, which has since reunited at Warner Bros. under the name Orion Pictures, for having a uniquely realistic outlook. "There're the only ones," he said, "who won't try to tell you that they know in advance what the audience wants. At Universal they'll say, 'Well, we put it in the computer, and the computer says it's going to be a smash.' It's nonsense. The computer they really wish they had is George Lucas' brain."

Lucas has insisted that he has "retired" or "dropped out" as a director. The idea seems unthinkable when you consider the enviable facility for the medium he displays, but evidently he means it.

It's possible that Lucas may be trying to reserve his directing energy for enterprises that require less time and stamina than "Star Wars." For example, he and Spielberg have hazy plans for a globetrotting adventure spectacle that the former would produce and the latter direct. Lucas plans to supervise a number of upcoming projects in the capacity of executive producer, official or unofficial: the first sequel to "Star Wars" now being prepared by director Irvin Kershner, a belated sequel to "American Graffiti" reuniting most of the original cast; a new comedy by the team of Willard Huyck and Gloria Katz, who rose to prominence as co-writers of "Graffiti" and then plummeted with "Lucky Lady."

Lucas is rumored to be discreetly but deeply involved in the editing of Coppola's Vietnam war allegory, "Apocalypse Now," whose costs are estimated to exceed $30 million and whose theatrical release still appears to be at least a year away. There are several poignant ironies involved. John Milius' original screenplay for "Apocalypse Now" was optioned by Coppola almost a decade ago with the idea that Lucas would direct it for the experimental production company Coppola had founded in San Francisco, American Zoetrope. The deal fell through and eventually Coppola took on the project himself. Now four years in the making, it may have become the kind of epic obsession that doesn't so much crown a career as exhaust it.

It's conceivable that Lucas could help liberate Coppola from the burdens of "Apocalypse." At any rate, he's in a position to return the favor to his erstwhile mentor who was the most significant force in American filmmaking five years ago. As long as it remains a benevolent creative influence, may this new Force be with us.