BROADWAY rehearsal studio . . . 45th floor . . . Manhattan yawning gigantically below the great window: Chrysler Building, Queens, Long Island, the sea . . . in the next room Niagara Falls roars. And a woman cries out. Sarah Berhardt has discovered America.

The taped waterfall clicks off, the door opens. Lilli Palmer is ready to break for lunch. She is doing "Sarah in America," a one-woman tour-deforce that opens its premier run at the Einstien Theater on Thursday. Palmer has not been on the stage in 14 years, but she is so excited about the idea of playing her great predecessor that she seems to have taken on some of Bernhardt's fierce drive. Her strong, energetic face dominates the white Victorian frills she wears.

Long before this play ever came to life, Palmer had been thinking about Sarah Bernhardt and the mystery of her fascination for Americans. The lifelong rival of Eleanora Duse, "the Divine Sarah" overwhelmed audiences from her first flamboyant success in a Victor Hugo play in 1872 to her death in 1923, revered as France's greatest actress.

"Did you know she spent a fourth of her adult years in America? People who know nothing about the theater still know her name. There's even a lake named after her near Spokane."

There was the cowboy who rode 300 milels to see Sarah Bernhardt act in Texas. When he got to the box office he said, "Say, what she do, this Bernhardt, sing or dance?" There were the thousands who clamored to see her great classic "Phedre" by Racine, all grand tragic gestures and rolling, heaving, sinous 12-syllable Alexandrine lines.

In French, of course: Sarah Bernhardt never spoke a word of anything else on stage.

She had a wooden leg, too.

"Those cowboys," Palmer muses, "whatt in God's name could they have been thinking? It must have been like a visit from a Martian. Her great speciality [Palmer speaks mostly British English] was the death scene. Death fascinated her. She carried her coffin around with her and sometimes slept in it because she wanted to face what she feared most." Once Bernhardt insisted on witnessing the guillotining of a man who had tried to murder her. ("Iforced myself not to look away at the last moment," she used to say. "I saw and I used what I saw.)

Death scenes can be tough on the ribs and shoulders. You swoon, you collapse in a heap, you crash to the floor, you fall into the furiture, you keel over backwards. "Physically, it's exhausting," says the 66-year-old Palmer, delicatley brushing a brown lock from her forehead. "I go from Sarah's 36th year to her 74th, and I'm running around like one demented. I'm on the stage the whole two hours."

"Sarah in America," by Ruth Wolff, breaks a lot of rules. It is one of the very few one-woman plays ever produced. And it is not your usual series of vignettes, insights and epiphanies of Bernhardt from her first visit to this country at age 36 to her death at 79. There are elaborate sets with three revolving platforms, sound effects ranging from Niagara to a roaring tiger, some 20 costume changes for tall, slender Lilli Palmer.

"I have a woman dresser there to hand me props, but she doesn't speak. I don't feel alone at all -- it's hypnotic, all those people I'm talking to, the customs man, my manager. I see them at different eye levels, some tall, some short. When the director says, no, this person should come in from the right and I've had him on the left, it's very hard because I still see him there."

A great comfort, she says, is having Sir Robert Helpmann direct, for the former ballet dancer (he was in "The Red Shoes" and choreographed the title dance) has a keen sense of choreographing for visual effects, for mime, for business to take the place of dialogue.

"It's probably a coincidence," says Palmer, "but this play comes on the centenary of Sarah's first visit to America. It's a love letter to America. She saw over 100 cities and did lots of farewell tours. In her last speech she told her audience, 'I survived your food and I even survived that tune they always play after "La Marseillaise," can you really be going to make it your national anthem? I even got used to that tune . . . '" Clearly, Palmer is in love with this play.

Palmer's own career, which took her from the stage in Berlin and London to Broadway and Hollywood, has alternated rhythmically between theater and film since the '40s. She quit the stage with Noel Coward's last play, "Suite in Three Keys," returned to the movies and made several in Europe as well as some choice Hollywood productions with the likes of Astaire and Gable.

"I sent back a lot of plays unread with a humble apology that it just didn't fit into my life. God forbid one would be a success and run all year. I did this one because it's a limited run and it's so crazy. But the stage -- I figured I was finished with that phase of my life. It would have been a repeat of the past."

The famous liquid eyes tht John Garfield would have died for in the 1947 film "Body and Soul" took fire. "I have so many eggs in my basket! So much to do and this one life to do it in! Like Sarah, who was a very good sculptor, you know. I'm a professional painter. I'm a professional writer. I've made more than double as much from my books as from all my plays and films put together!"

The German-actress has written two novels and her autobiography, "Change Lobsters and Dance," a thundering best seller now in 18 languages -- "720,000 hard-cover copies sold in Germany alone!" -- a lively romp with lots of names, from George Bernard Shaw to Helen Keller, and unabashed frankness, also some gushings like ". . . my father, who had spent four years at Verdun during the First World War helping defend . . . the fatherland he loved . . . " (The battle of Verdun didn't start until February 1916, and a German named Peiser was unlikely to have been defending his fatherland in France. Oh well.)

This book is rather like Lilli Palmer herself, in fact, an intriguing mixture of artist and star. Taking about the early years in Berlin and London (the first big break was in Carol Reed's 1939 "A Girl Must Live"), she can sound self-consciously girlish. But then you read her harrowing account of her breakup with Rex Harrison (they had married in 1943), his love affair with Kay Kendall, his decision to divorce Palmer and marry the English comedienne because she was dying of leukemia, the orderal of appearing with Harrison in "Bell, Book and Candle" to honor a London contract -- "embracing each other every night with wooden arms" -- and he telling her, "Maybe you ought to have a lover. Maybe that would help you."

Palmer has juggled her lives with skill and aplomb. The first Hollywood period, in the late '40s, saw "Body and Soul," Fritz Lang's "Cloak and Dagger" and a war with movie gossip writers when Harrison's name was brought into the Carole Landis suicide. Then back to Broadway, Harrison scoring in "Anne of the Thousand Days," Palmer landing the stage role of her life in the 1950 production of Shaw's "Caesar and Cleopatra." For this , she went to England to see G. B. S. himself at 92, and her account of her visit is a high point of her book.

Awed at "sitting right next to this old boy who was sitting next to Oscar Wilde the day before he was arrested," as she said, she nevertheless charmed him right to the point that he showed her the famous chicken coop where he did all his writing ("the table was meticulously tidy, with a stack of paper, a few pencils and pens, and, on a blotter, a pair of mittens") and cackled as she drove off, "Well, did I give a good performance?"

Returning to the movies in 1952, she and Harrison made the film version of "The Fourposter." They were divorced in 1954, and three years later Plamer married Carlos Thompson, an actor and writer. "We've been together 26 years now and still terribly happy. Nobody will believe a thing like that. Nobody tries hard enough these days. You have to work at it. That's what they don't understand. The young seem to sit back and say, Come on, entertain me."

The final Hollywood period, in the early '60s, wound up with "Counterfeit Traitor" with William Holden. Her non-English pictures include the French "Le Residencia" and the East German "Lotte in Weimar."

Most of the time she and her husband live in a hotel facing Central Park in New York, where they can walk their enormous black dog, Schlemeil. There is also the villa near Zurich -- "but I'm never there long enough to really unpack. Travel? . . . " the eyes roll . . . "In my dreams I fasten my seat belt! But after this play closes, the 15th of June, I have canceled everything to the end of the year. I'm going to just live!"

Lovely. You can see her with her feet up on the recamier watching her thumbs chase each other for six months. Sure.