THE good citizens of quiet Lakeville, Conn, go to bed early--with one exception. But even the rare, late-homecoming villager is no longer surprised at the single globe of light shining from the ungainly green-and-yellow hilltop house which broods over the main street. He knows, along with those of his neighbors who have seen it, homeward bound from a church supper or Saturday-night movie, that Mme. Wanda Landowska is at her devotions: her altar, the harpsichord.

Pint-sized (4 ft. 8 in.) Mme. Landowska, 73, is unchallenged high priestess of the plunky, double-keyboard instrument for which Bach wrote, before the piano supplanted it in the 18th century. Under her dedicated leadership, the harpsichord is having something of a revival, and her recording of Bach's Well-Tempered Clavier is already a modern classic. Next week RCA Victor will release its fifth album, leaving her one album still to do.

Even when she works into the small hours of dawn, Mme. Landowska wakes at 8. Coffee and correspondence are brought to her bed by Denise Restout or Elsa Schunicke, who for years have served as adoring disciples, companions and helpers to "Mamusia" (Polish for mummy).

When she has answered her letters, Wanda Landowska is ready to descend. She loops her long, still-black hair, only sparsely greyshot, around her head, dons her blazing red corduroy robe ("red is for violence, like Bach, sometimes"), her flat, gold-mesh slippers and goes down to the kitchen for a breakfast of figs, dates and lettuce.

Several hours at the harpsichord later ("I never practice, I always play"), Mme. Landowska takes an hour's walk around the countryside. Neither rain nor snow stops her from venturing outdoors among the Berkshire foothills she has loved since first she came in the summer of 1947.

In cold weather, cocooned in several layers of shawls and scarves, and wrapped in a huge old overcoat, she sallies forth. Her hands nest mandarin-style in the large sleeves. Each day's walk ends the same way--with a visit to her "last sweetheart," an 80-year-old carpenter of Lakeville. "I spend my relaxation ration with him. We understand each other --we are both craftsmen: he loves his carpentry as I love my music. Our conversation is very condensed." With a birdlike flutter of her thin-boned hands, Landowska adds: "But his niece --she is too bourgeoise. She does not understand why I am there every day. She is shocked, even now."

IN Warsaw as a child of four, Landowska expressed herself on the piano while other children were learning to talk. Her first teacher, recognizing her precocious virtuosity, let her play whatever music pleased her. But "a stern, dry man" took his place, and "my delightful roamings through the gavottes and bourrees of Bach were at an end." She was very unhappy. "I dream only one thing, when I am grown to play only Bach, Haydn and Mozart." She sealed this vow in an envelope, to be opened "when I am a big girl. But I opened it the next day, of course."

She graduated from the Warsaw Conservatory of Music at 14, an accomplished musician whose professors agreed that they had nothing further to teach her, and set off on her own, giving concerts throughout Europe. But Landowska had no desire to dazzle concert audiences in the accepted manner: "I have always been in revolt." Her beloved cantor of Leipzig, Bach--and his contemporaries--had vanished from the piano repertory. Instead, performers who believed that the old master had no notion of the keyboard's capabilities served up a hybrid fare under the names of Bach-Liszt, Bach-Tausig, or Bach-Buelow. "They put Bach, Mozart, Handel back on the loom," Landowska buzzed in her book Music of the Past. "And after calumniating the greatest masterpieces, they dare couple their obscure names with those of our supreme masters . . . What would sculptors say if a mason undertook to cut away some marble from the Venus de Milo to give her a wasp waist, or if one tried to twist Apollo's nose in order to give him more character?" The first thing to do was to remove the overstuffed romantic upholstery from the original music. The second was to rediscover the true harpsichord in place of the "little gavotte players, toys for wealthy amateurs" constructed at the turn of the century.

TOGETHER with her husband, Henri Lew-Landowska, who hyphenated his name and identity to hers, and was a folklorist, an amateur musician, "an excellent cook" and her personal court jester, Landowska began collecting manuscripts and examining old harpsichords in all the great museums of Europe. She brought the results of her researches to the Pleyel firm of Paris. In line with her suggestions, they built an instrument, "capable of greater brilliance and more tonal variety --the first modern instrument to give full justice to the 16-foot register, that essential set of strings for a deep resounding bass."

In 1907, Countess Tolstoy heard her play in Moscow and invited her to her estate for the Christmas season. The count sent two sleighs to the railway station, one for Landowska, the other for the harpsichord which has followed her everywhere, sometimes on gondola and camelback. She returned again for the Christmas of 1909: "My music was a revelation to Tolstoy. I played for him; he talked for me."

For 20 years, the jangle and warble of her strings was heard at Saint-Leu-La-Foret, a green suburb of Paris where Landowska established her Ecole de Musique Ancienne. Here she lived, after her husband's death in 1919, among her 10,000 books and manuscripts, her pupils, her ancient instrument and nine dogs. Music lovers from all over the world came to her villa and concert hall. The 2 o'clock train that left Paris every Sunday for Saint-Leu, 30 minutes away, was referred to by station guards as "Mme. Landowska's train."

IN 1940, she fled the Nazis who looted Saint-Leu of everything she owned. She escaped to the south of France with only some photographs of Tolstoy, several sketches given her by Rodin and the clothes on her back, and went to live at Banyulssur-Mer near her friend, the sculptor, Aristide Maillol. The only instrument in her pension was a battered old upright piano. Late one night, when everyone else was in bed, she sat down and played until morning. When the proprietress came down, Landowska inquired whether her playing had disturbed her. "But no," she replied. "I do not sleep well since the war, but your banging put me to sleep."

Since Mme. Landowska came to the U.S., her favorite harpsichord, the Pleyel, made especially for her and inscribed with her name, has been found in a Bavarian castle.

Although she has made as many as 150 concert appearances in a season, Mme. Landowska now rarely appears in public. "At last I have learned the key to the mystery. I must be concentrated about my work." Most of her time is dedicated to making her recordings of Bach's Well-Tempered Clavier, her "last will and testament."

Landowska's brown eyes still kindle in the ashes of her face at the mention of her "ghosts." This small empress in exile from her time has lived with them for most of her life. For her they are alive. And it is entirely conceivable that if one day her door should open, bringing a visitor named J. S. Bach into her instrument-cluttered, timeless room, Wanda Landowska would not so much as lift her bird's-wing eyebrows in surprise. She would probably continue the conversation she has been having with him across the strings for the past half-century.

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