NOW AND THEN a show bursts onstage which envelopes its audience in the exhilaration and pain of a lifestyle very unlike their own.

A Chorus Line, the long-running musical dramatization of a Broadway audition, is just such a masterpiece. As each of the aspirants rise to audition, exposing their secret dreams and their desperation, their message becomes most intense: before long, we too are backstage, yearning for even the briefest chance in the spotlight.

Since its opening in 1976, A Chorus Line has broken box office records on three continents, captured nine Tony Awards and the Pulitzer Prize for drama: now it returns to the Shubert Theater for its fifth and final engagement. The curtain has risen for more than 3000 different audiences. In more than 3000 performances over seven years, the show's international company has not lost its spark: in this engagement the dancers and singers perform with the exuberance and energy of an original opening night. All the ingredients that have made A Chorus Line so successful remain strong in this production.

But A Chorus Line is not only a play about the hardships of an artistic life: it also depicts a coming together of individuals, the creation of a community. The dances begin the long screening process, which will eventually whittle the 28 applicants to a final company of eight, as strangers, linked only by their love of a common career. As the audition progresses, and they are forced one by one by the demanding director Zach (Eivind Harum) to reveal their anxieties and fantasies, the actors draw closer. By the time the final selections are made, they have formed a supportive brotherhood.

Their dancing reinforces this progression towards unity. In the first number. "I Hope I Get It," the cast performs deliberately offcue. Each time a dancer stumbles or misses a step, he winces with disappointment, and glances at the competition. When Zach later asks them to introduce themselves-- "I just want to hear you talk and be yourselves"--they freeze: this is an unexpected, personal request, and as the lights fade the artists cover their faces with promotional photos, hiding behind the confidence of a typed resume.

But as they draw emotionally closer in the audition, the dancers symbolically fall more and more in step. Their songs become joint expressions, not individual cries of emotion. We are watching the creation of a synchronized chorus, and by the final reprise of "One," the company taps and twirls as a single unit, their feet linked by invisible thread.

LIKE ANY PLAY with no individual stars. A Chorus Line depends on a fine close-working company. Almost all of this cast are stunning, but a few shine above the rest. Diana (Mary Lou Crivello), as a tough but warm kid from the Bronx is delightful; he solo "Nothing," about her frustration and growing confidence as an actress, is uplifting and powerful. Among the men Mike (John Dolf) and Richie (Woodrow Thompson) stand out for their fast footwork, strong voices and sheer exuberance. And Val, played by Lois Englund, excels in the bawdy "Dance: Ten: Looks: Three," as the once ugly duckling who found strutting success through massive plastic surgery and silicon-induced "tits 'n ass."

But when Pamela Sousa as Cassie dances with the company, they fade from view. Although her voice strains when belting out the powerful "Music and the Mirror," on the dance floor Sousa is music itself. She explodes with energy and spirit and handles the difficult transition from fast jazz to sensual, seductive contortion with astounding grace. Surprisingly, Sousa is only an understudy for the regular Cassie, Angelique IIo.

As an actress, Sousa is also remarkable. Zach's one-time lover who left the chorus for an unsuccessful Hollywood career. Cassie returns to his audition full of sadness and desperation. In the end, the musical's triumph is largely her own; she wanted to be a dancer. Zach had wanted her to be a star, and in A Chorus Line, Pamela Sousa finally is both.

THE CONSISTENTLY CATCHY and poignant score, with music by Marvin Hamlisch and lyrics by Edward Kleban. James Kirkwood, and Nicholas Dante still holds up. Only one number falls flat: "And..." which was rightly omitted from the best-selling album, is a dragging combination of monologue and medley that leaves the viewer cold.

The equally time-tested setting is an empty stage, and the props are limited, but the placement of large practice-room mirrors and the variation of harsh white light with soft rotating colors more than compensate for the space decoration.

The most moving episode in A Chorus Line, and also the one in which the artists finally share their professional anxiety, comes with the song, "What I Did for Love." Paul (Wayne Meledandis) an ex-drag queen humiliated by his past, pulls a ligament in his knee and is carried off. The remaining dancers fall silent in shock: Paul's accident forces them to consider the instability of their career.

"These bodies don't last forever," one comments. As the others nod and tremble, Diana steps upstage: "Nobody got into this business to play it safe," she reminds them. "We're all here because we love it."

Perhaps A Chorus Line has remained so vibrant because, after seven years on the road, it still is able to make us see why.