The Wintergarden Room in the Embassy Row Hotel is packed this rainy Friday night as pianist John Eaton, his eyes on the singer, launches effortlessly into "Easy Living." The intro is casual and gentle, in Eaton's deceptively offhand style, but after about six bars he abruptly stops.

"Wait a minute, wait a minute," he mutters to himself, pushing his glasses back with his middle fingertip. He starts again. Only one note is changed: an interval of a third has become a fifth, reaching dramatically higher. It utterly transforms the music, gives it shape and force.

The audience doesn't notice. They love the song, though. They give it a great hand.

If you call John Eaton a cocktail pianist, you just aren't listening. True, after 25 years of it you have to call him the dean of Washington piano bars. But if you're thinking of someone who vamps a few chords and campy glissandos around a show tune, you're thinking of the wrong guy.

The great jazz pianist Marian McPartland says, "He'll pick a song and twist and turn it, and hold it up to the light, and then polish it a little as if it were crystal."

When Eaton finally favored New York with an ongoing gig at Hanratty's, local critics started talking with wild surmise about Art Tatum, Fats Waller, Thelonious Monk, Alec Wilder and James P. Johnson.

George Shearing calls him simply "the best pianist in Washington."

For the past seven years his lecture-concerts on American popular music, broadcast around the country, have swamped the Smithsonian with ticket orders, selling out almost the day they are announced.

Listen to his version of "Night and Day," or anyway the version on one of his four solo records, for every time he plays a song it comes out a little different. It's as though he were just discovering this old warhorse. You think, This must be the way Cole Porter first heard it as he put the notes together with his questing fingers.

Hear him do "Send In the Clowns," which you have heard many too many times: He can still raise the hairs on the back of your neck. And "Wunderbar," that galumphing Porter waltz: Suddenly it has a sweet fragility you never knew was there.

A minute later he roars into "Fascinatin' Rhythm" with such drive and energy you would swear Oscar Levant was playing, or maybe Gershwin himself . . .

The thing about John Eaton is that, with all the talk of Tatum and Waller and Bill Evans and other jazz pianists he admires, his music always comes out John Eaton.

Laconic, even diffident at times, playing with his friends at the Wintergarden, he lets his superb string bassist, Tom Cecil, accompany singer Linda Cordray for many bars, adding only a single chord now and then. Then he gives clarinetist Wally Garner what amounts to an extended solo, coming in with the odd phrase, the harmonizing bass, the occasional friendly note that turns the music into a conversation between a couple of old pals.

"When you're playing with players like these, you don't need a drummer," he tells the audience. "If we had Ringo Starr here we'd let him water the flowers."

The garden theme runs through his patter all evening. He talks to no one in particular, perhaps to himself, musing quietly in the low-voiced manner of Garrison Keillor. Finishing one number -- a brilliant duet with the clarinet -- he mutters, "What'll we call that? 'Embassy Row Your Boat Ashore?' 'Jousting at the Wintergarden?' " Someone calls out, "Or mulching," and he chuckles. Between songs he whispers almost inaudibly with his group about what they're playing next and what key they want.

Linda Cordray puts on her glasses to read some lyrics she typed herself. It takes a while to get her voice warmed up, but she sings with such assured style that it doesn't matter. You could be in her dressing room, sitting on a folding chair beside the mirror while she does her eyeliner.

For that matter, with John Eaton & Friends, you could forget you were in a hotel bar at all. It might be a rainy weekend in front of a fire in somebody's big shingle house at Amagansett.

"Sensitive" is a favorite word of his critics, also "witty" and "graceful." The word you hear the most, though, is "surprise." The lovely ideas he gets as he takes off from, say, "Small Hotel" or "Ain't Misbehavin' " or some other standard, the sly quotes from Bach, the boogie-woogie that slips in, the droll recasting of "Old MacDonald" as blues, all these inventions can turn the most familiar song into something of his own, something never heard before.

Always, he sounds spontaneous. But always, he is in control. As he says about his friend Cecil, "He knows where the music is going before it goes there."

"I played piano when I was a kid," he says. "I went to Landon, graduated from St. James and Yale, and at that age, if you can play piano it's an entree, you're in, you don't have to bother about conversation, communicating with girls. You can sit down and hide."

He was an English major. He was going to teach. One of his grandfathers was president of Cornell, another founded a pioneering political newsletter. One of his grandmothers was a Welsh Quaker who eloped to go on the stage in London in 1870. His father, a newspaperman, came to Washington in the '20s, and it was here that John Eaton was born 50 years ago.

"After Yale I did a year of graduate work in English at Georgetown, didn't like it, and then I went in the Army. Already I'd been playing more or less professionally in the area, and when I came out, there it was. Amazing what you'll do at 24."

Eaton and Wally Garner and some others played at the Bayou, then a jazz club. They formed their own band and settled into the Mayfair for three years, and from there Eaton moved to Blues Alley, the Potomac Room, the Snuggery and half the piano bars in town.

"It's a curse in its way," he says. "You know it's the only thing you want to do, but it's an excuse for not doing something respectable. The older I get, the less respect I have for the respectable professions."

Just the same, for 25 years he took lessons in the classical repertoire from pianist Alexander Lipsky, who died in June at 85. "A great pianist, an incredible pedagogue. He took me, a semiliterate jazz pianist, barely able to read music, he saw my potential, and in a way he made my career, because what I do on piano now is due to his teaching." The real secret of being a musician, he says, is learning how to hear.

He tells the story of how the kind but sternly demanding Lipsky once actually admitted that he was "a very good pianist, outstanding in your field."

He shrugs. "I'll never be the classical pianist I want to be."

On the rack of the grand piano in his study at home (across from an old upright) is a book of Schumann sonatas.

His branching out to New York and to Arthur's in Miami was a watershed in his career, perhaps, but his abiding interest today is in teaching. He has given 70 lectures at the Smithsonian and is going on the road with that program soon, and in time he hopes to hit the college lecture circuit.

He has a lot to say.

"So much of what you hear is wall-to-wall junk. And one reason is, there's no comparison factor. People's musical education is abysmal. They don't know. I try to get people to listen to songs from the Gershwin and Ellington era, teach them musical values. What it is that makes the songs culturally worthwhile."

Passion is not enough, he says. The decline of pop music began in the '60s ". . . and left the way open for these awful people in the music business now. There was something honest and earnest there for sure, but you now have people who cannot hear, who can't hear musical values. They get this hunger to experience good music, and they wish so hard for it to be better than it is that they impute things to it that aren't there."

He finds Andrew Lloyd Webber "a total charlatan who writes synthetic music he borrowed from everyone else," and when he's asked to play something from Lloyd Webber's "Evita," he tells the audience he'll do a number from the (nonexistent) third act, written, he adds, by Benny Goodman. In this scene, he says, Che Guevara does a dance for Evita and changes the course of Argentine history.

Then he glides into "Stompin' at the Savoy."

"It's a wonderful test of an audience," he says. "Some of them, it goes right over their heads. I'm sometimes accused of not keeping up with the newest Broadway stuff, but what do you do when you have to get with It and there's no It to get with?"

He talks about taking risks. This is central to his work as an improviser. The risk-taking in jazz is something that should be in all music, he says. "Artur Rubinstein, every performance, he started from scratch. You could hear him taking chances. It's the way it should be. Instead of the safe conservatory way."

Sometimes, with an audience he doesn't know, he plays it safe, falls back on things he knows will work. He never plans a sequence of songs in advance, but he may do a medley from audience suggestions, combining "Sweet Georgia Brown" and "Laura," for instance, in a way that elegantly points up their similarities and disparities.

"Too much order kills your spontaneity. The greatest moments come when somebody suggests a tune and you play it, and all of a sudden this world opens, you can feel it happening: It isn't the tune you'd thought of playing, but something new. And you can feel the audience responding."

He practices three or four hours a day. Until two years ago he had a stable of 30 students, but he is now down to three. Each Smithsonian concert means at least 40 hours of preparation plus a certain amount of psyching up.

He lives in a modest house behind American University with his wife Penny Carr, a creative director with Time-Life Books. His two children by a previous marriage are grown up. "I have no intense hobbies," he says. "I'm not a Walt Whitman scholar on the side, I don't grow violets. We do love to walk and we travel, but music is my life. Music is it." He shakes his head deprecatingly. "What a complex man!"

Oh yes . . . the Horchow records. According to legend, two John Eaton records are listed in the Horchow Collection mail order catalogue, one of those Dallas outfits catering to people who have everything.

Is this true?

"Well, Roger Horchow was Class of '52 at Yale," he says, "and an old musician friend of mine had terminal cancer, so Horchow asked him to do a record for the catalogue. A lovely thing to do. I wrote the liner notes for it -- that was how Horchow found out about me. He heard my stuff on Chiaroscuro Records and liked it and offered to put me in the catalogue.

"I noticed Marian McPartland had done one for him, so I called her up and asked. 'Is this a good idea? Good for my image?' Well, Marian curses like all good English majors. She said, 'You expletive idiot, of course! Do it! That thing goes to 20 million people!"

So there he is, exclusive in the latest Horchow catalogue, among the Chinese screens, snakeskin belts, desk-top barometers and monogrammed glasses and other stylish surprises. Somehow, it's very John Eaton.