MIDWAY between Central park and Broadway on West 61st Street sits an unpromising building with a black facade; inside, flesh-toned walls flake onto grimy carpeting. A senile elevator ascends slowly to the seventh floor, where Mikhail Baryshnikov and some seventy-five members of the American Ballet Theatre rehearse The Nutcracker and other balletic spectaculars for performances at the Kennedy Center December 6 to January 1.

Dancers lounge on steps leading up to a viewer's gallery, some do needlepoint, others read the paper, a few pick up salary checks from a pixieish woman wedged behind a desk. A leggy blond winds her hair into a chignon and fixes it with hairpins, while a male dancer hikes up plastic leg warmers over thick black tights.

Mikhail Baryshnikov peers out from under shaggy bangs and sips coffee, quietly awaiting his turn at the dressing room where he will exchange a red-striped pullover and beige pants for navy practice garb and a zippered jacket. Gelsey Kirkland, pony-tailed and snapping gum, intermittently draws on a thin, brown cigarette and exhales huge puffs of smoke.

On the surface, things are calmer at ABT's New York home than news reports in recent years might suggest. Kirkland and Baryshnikov are reunited on the stage, she seemingly recuperated from a long spell of ill health, and both apparently recovered from rumors of their short-lived romance.

"Union meeting in studio one!" Languid bodies spring up and disappear into a meeting barred to all but union members. Company dancers belong to the American Guild of Musical Artists. Last fall stymied contract negotiations almost precipitated a dancers' strike.

Union regulations stipulate minimum weekly starting salaries at $493 for principal dancers, $380 for soloists, and $235 for members of the corps.

The corps de ballet serves the same funcation in a dance as a chorus in a mucical. It is also the proving ground for aspiring soloists.

"I promote somebody who looks so good the rest of the corps is glad to see them go," says Lucia Chase, cofounder of the company in 1945 and still emphatically its director. With the erect posture and slender figure of a former dancer, she watches rehearsals from a stiff-backed wooden chair, conferring in whispers with rehearsal directors, and making notes.

Michelle, Kristine, Carla, Janne, Lisa, and Cheryl - apt names for the petite, pretty girls who bear them; they know Lucia is there, recording, weighting, judging. "I look for good technique, and projection - the dancer's effect on an audience. Former awards and credentials mean nothing here," she insists, and all dancers must spend time doing yeoman's duty in the corps - with a few exceptions.

The most recent exception is nineteen-year-old Leslie Brownie, whose dark, serious eyes enhance a porcelain frailty. Chosen to play opposite Baryshnikov in the recently released "The Turning Point," Leslie was hired by ABT as a soloist, having never served in its corps. According to some critics, her potential is as yet unrealized.

"Leslie Browne . . . that is a very touchy subject, especially for members of the corps," hesitates a dancer elevated to soloist status in 1974 after two years in the corps. Black tights accentuate her long legs. A full, reddened mouth shines like a poppy out of a translucent complexion. "There can be only so many soloists, and with money so tight right now . . ."

"I had to tell the girls this year that because of financial difficulties, there would be no raises in salary and no promotions," affirms Lucia Chase.

"We talk among ourselves that it is hard to have a social life. But I don't find it frustrating because I spend the day doing what I love, not just a job to earn a living," muses one dancer.

"Dancing is my life," says another, plainly. She began studying ballet as a small child in the Caribbean and South America. At eight, she was sent to boarding school in New York at the National Academy of Ballet and Theatre Arts and joined ABT after graduation. It's a cloistered, disciplined life. The attraction is almost the attraction of a formal religion. Every movement has its name, its meaning, its function.

Rehearsals are in session from 11 a.m. to 6 p.m. six days a week and performances and traveling afford little opportunity and leave even less time for meeting people outside the world of dance. It is not surprising that hothouse romances blossom and wilt among members of the company. Kirkland has described it: "Everybody tends to get involved with everybody else, especially the young girls, and there's a lot of jealousy and tears and heartbreak . . . if you get hurt, you know you still have to go on working with the same person on stage."

Moppets in blue leotards and pink tights and shoes wobble through a glissade, pas-de-chat (a slide and jump) variation. They mimic the sequence, but their unformed bodies lack the definition of movement that marks muscular control and strength. The school associated with the company conducts public lessons on a pay-as-you-go basis and scholarship classes by audition only.

Students in the open class range from a rouged and powdered housewife to long-haired George de la Pena, a soloist with the company.

"Ohhhhh, George is sooooo cute," squeals a prepubescent ugly duckling. "If I had my choice, I'd marry him tomorrow."

Lucia Chase: "We like coming to Washington. It's a different city since the Kennedy Center. The Opera House floor is good for dance, but I wish there ere more seats. We need a 3000-seat house to break even, and the Opera House only has 2300."

A young dancer: "We look forward to coming to Washington because more of us get a chance to perform. In New York, they don't fool around; the stars go on because the audience is hypercritical."

An experienced woman dancer squints out of puffy, Saturday-morning eyes and tucks brown curls under a pink hair ribbon. She takes her place at the far right of the studio and becomes a tree in the wind, circling her arms and body, but remaining stationary, her sinuous movements formal, depersonalized. Suddenly, a male dancer falshes across the front of the studio in high, sharp jumps and leaps. Atonal music issues from a tape recorder.

"Sometimes people say I make abstract ballets. They're never abstract to me," puzzles tall and balding Glen Tetley. his piece, to premiere in Washington on December 9, is still under construction.

The two dancers run toward each other; he catches her mid-air in a lift, tosses her over his head, and supports her on his other side as she alights. Perspiration soaks through in dark patches on her cocoa-brown leotard; sweat drips off his nose and mats his hair.

A tee-shirted male dancer swaggers by, pausing to glance into the studio. "What's THAT?!" he sniggers. "Creature feature?!"

Gelsey kirkland soars through the air in a high split jump, her lightness belying the control and strength that support any well-executed leap. Lighted cigarette in hand, Baryshnikov raises her in a lift. Her slight body seeming to float down into his arms.

Rehearsal for "Graduation Ball," a light one-act ballet being revived for presentation in Washington: "More arthritic! Everything hurts you!" A swarthy male dancer locks his knees, stiffens his back, and stumps in, an old general leading his young cadets to a dance at a girls' school. The headmistress - a man's role - flutters his/her eyelashes at the general, who arches a brow and leers back.

"Twirl your mustache!" They general fingers his imaginary mustache and ogles the unshaven headmistress. The cadets break up.

"I'm happy here. I never miss Russia!" declares Sacha Minz, the headmistress, mopping his face with an orange towel. A Jew, he was thrown out of Leningrad's Kirov Ballet after applying for emigration papers. Like many Russian-trained dancers, he excels at character roles which require acting and mime, although he can imbue more serious romantic roles with a fine lyric poignance.

Each hour on the half hour, dancers dash out of one studio, consult the day's schedule, and dart off to another studio for another rehearsal. But by late Saturday afternoon, two studios are dark; in a third, a lone dancer whirls across the room practicing pirouettes. Many dancers, through for the day, have left.

Five weeks remain before the company arrives in Washington, and myriad non-dancing logistics require attention. Transportation must be arranged and accomodations found - usually at the Watergate or Guest Quarters on New Hampshire Avenue - for almost 100 people, including the conductor who periodically attends rehearsals. (The conductor keys the tempo of each piece of music according to the way the dancers count it; during performances he leads locally recruited musicians, keeping his eye and ear attuned to the pace onstage and making necessary adjustments.)

Sets and costumes remain to be unearthed and shipped from warehouses in Philadelphia and New YorK. And the final program details and schedules are to be negotiated between Martin Feinstein, Kennedy Center Executive Director for the Performing Arts, and Lucia Chase. "Martin doesn't want anything that was done on a Friday night last spring done on a Friday night this winter. I think that is so series subscribers don't see the same thing."

"Hey, you think I live here?" complains the elevator man. "I been here twelve hours already. Time to go." He cajoles three dancers onto the elevator. "Time to go."