WHAT IS THERE about the hungering and wanderlust of young American males that's so distinctive in flavor - that makes Huckleberry Finn and Dreiser's George Eastman and Holden Caulfield and "The Glass Menagerie's" Tom and James Dean's causeless rebel and so many of their fictional brethren so alike despite their differences? What is it that binds them together as a restless breed, so indelibly of this country, and sets them apart from their analogues in other climes and cultures?

Yes, there's the cutting of the cord that has been part of our history from the time of the colonials and the Revolution; there's the ever-beckoning frontier, the root myth of the nation; there's the elusive phantom of "upward mobility", there's the sectarian quest for the ideal that has replaced established creeds in our society, and all of this impacting on that of life that is most vulnerable to fantasies of discovery and conquest. And there's more: The proximity, in our cities especially, as well as in medialand, of the haves and have-nots; the material plenty, an incitement but also a turn-off; and that Emersonian notion of self-reliance and bootstrap ascent that has fed the ambitions of young men from Daniel Boone to John Travolta.

John Travolta? Whatever this common inheritance may consist of, it can be seen and heard and sensed, if not precisely defined, in both "American Graffiti" and "Saturday Night Fever," which thanks to the fact that the movie business rarely misses an obvious trick, are to be found playing virtually side by side in area theaters these summer days.

It's a fascinating juxtaposition from a great many standpoints. Both films were "sleepers," relatively low-budget features that nobody expected to take off but that skyrocketed anyway at the box office, though neither picture had the advantage of known stars. Both were made by young, practically neophyte directors - John Badham for "Saturday Night Fever" and George Lucas for "American Graffiti."

Both are basically celebrations of the rites of passage from adolescence to adulthood, in their quite separate ways. Both are in the nature of nocturnes, too - "Graffiti" covers a single night from roughly dusk to morning and "Fever" has some daytime scenes, to be sure, but both come alive woth darkness and noon, when pulses beat to the promise of mystery, eros and carousal.

The night in "Graffiti" is unspecified, but it too feels like Saturday - it has that feeling of the Saturday night mystique of American popular culture, when the young are on the make en masse, everyone's out prowling for adventure, and all, in a sense, are feeling loneliest as well, smitten with those unfillable romantic longings that Thomas Wolfe divined so poignantly.

The casts of both movies run a similar gamut of types, evening those sessions when one rifles through one's old high school year book, picking out the class romeo, the class clown, the class misfit.

The central figure in "Graffiti" is Curt (Richard Dreyfuss), a bright, sharp loner who's everyone's pal but has the instincts of a seeker, a poet, chasing after an ephemeral rainbow symbolized by the tantalizing anonymous blond in the T-bird (Suzanne Somers). His counterpart in "Fever" is the ambitious Tony (Travolta), king of the local Bay Ridge disco, who hides finer stuff under a veneer of vanity and bravado.

In both films there are girls who are easy on the draw and those who have their eyes fixed on more solid commitments - Laurle (Cindy Willaims), the conventional girl-next-door "steady" in "Graffiti," and Stephanie (Karen Lynn Gorney), the determined climber of "Fever." Both have a sympathetic runt - Toad (Charlie Martin Smith) in "Graffiti" the likable schnook who's forever feigning the macho expertise he craves, and in "Fever," Tony's scared little friend who falls to his death from a bridge trying to show he-s got "guts."

Most of all what the pictures share is the sense of these kids reaching beyond their horizons, itching to go primed for making it, busting loose, moving out, moving up. Tony, in "Fever," hankers for the big time,which to him means someone Stephanie, who's made the great leap from squalid Brooklyn enclave to glittering Manhattan. Curt, at the start of "Graffiti," says to his buddy Steve (Ron Howard), who's slated to depart for college from the small California burg that's their home, "So, friend you're finally getting out of this turkey town." The remark sets the prevailing undertone for the whole film, and at the end of course it's the questing Curt who leaves and Steve who stays behind. The goal of splitting from "turkey town" is what keeps both pictures on the run.

One other conspicuous elemenet the films have in common iis the use of pop dancing and music as a metaphor for restlessness, movement and yearning.

Neither movie is a "dance film" or a musical, but both are drenched in steps, sounds and beats of their respective eras, rock 'n' roll in the one and disco in the other.

Though Travolta plays the hot-shot dancer of his neighborhood, he's clearly no dancer himself - his performance never even has the natural animal rhythm one can see almost at random on any disco floor (his acting is another story, deserving of all the kudos he's received). And, as critics have pointed out, the dance scenes in "Fever" are messily cut, so that no single dance sequence ever takes hold. On the other hand, John Bode's smoldering cinematography really does catch the obsessive, hive-like ambiance of the disco (it was shot on location at an actual Brooklyn club).

The sock-hop scenes in "Graffiti" are evanescent and impressionistic too, but in this case Haskell Wexier, visual consultant for the film, has given us a model of how to convey the line, the lilt, the feeling of dancing with a movie camera. The point, however, is that both films carry the sensation of dance movement into their very texture all the way through, not just on the dance floor - as visual experiences they have the cadence and torque and flow of dancing.

In other ways, the movies are literally a world apart - they're divided by everything that separates the Pacific from the Atlantic, the 50s from the 70s, JFK's Camelot from Jimmy Carter's southerncomfort.

"Graffiti" is unmistakably Californian; nine-tenths of it takes place in, or under automobiles, which play the same sort of role in this film that the Big Brother computers did in Lucas'earlier feature, "THX 1138," and that spaceships and robots do in his subsequent "Star Wars" - they're the technological icons that give the depicted universe its stamp and focus. The movie also consciously dates itself with its carhops on roller-skates, its "mooning" its faddish expressions like "boss" and "knuckle sandwick".

"Fever" is, by contrast, all grubby, urban Brooklyn of the 70s, tough, ugly, nerve-racked by ever-impending violence of one kind or another. Some have been turned off by the scabrousness of the script, but the language is dead accurate, and so is the whole atmosphere of a New York ethnic subculture.

The movies have similar weaknesses - both meander ar times awkwardly, "Graffiti" cruising through its scenes with some of the same merrily aimless tacking of its own hot-rods, "Fever" scuttling frenetically from spot to spot like its erratic characters.

But individual flaws apart, both films strike one as possessing the qualities that make movies endure. Both exhibit exceptional sensitivity to the insignia of time and place, both have captured patterns of consciousness that ring true. And both are apt to haunt future generations with their resonant soundings of young American manhood in contrasting circumstances, linked by that incurable hopefulness perhaps best summmed up by the bromide, "The sky's the limit."