John Malachi tickles the ivory of a 100-year-old Steinway in the basement of his Northeast Washington home, preparing for back-to-back performances next week. With the musical score for the Kennedy Center's production of "Idiot's Delight" on one side and sheets of music for his concert at the Duke Ellington School of the Arts on the other, Malachi faces what appears to be an impossible task.

His concert is Sunday and the play opens Monday. With new music arriving almost daily and score changes being made almost hourly, he sometimes just sits and taps out the tunes of a man with a whirlwind of melodies in his mind.

"This is crazy," he says, pondering the ebb and flow of a river of notes before him. "The time . . . the time is so short."

But for a person trained to play in time, be on time and, when necessary, change time, Malachi, at age 66, is having the time of his life. This is his 50th year as a professional musician in Washington, and his popularity appears to have surpassed the days during the '30s, '40s and '50s when he was a regular with such greats as Billy Eckstine, Billie Holiday, Sarah Vaughan and Pearl Bailey.

Although his name never became quite as "big" as those he played with, Malachi has demonstrated extraordinary staying power and versatility. Part of the reason is that he decided early on to teach, and now excels in that capacity as a professor of jazz studies at Howard University.

The secret to his success, and lesson No. 1 to his students: dedication to the instrument.

"So many kids today think in terms of idols -- they want to be like somebody, do what so and so does," Malachi says. "But to survive in this business you have to be a master of your trade. You have to love the instrument you play."

Malachi was 13 years old when he fell in love. That was the year his father came home with a piano that had cost $5.

"It was six o'clock in the evening and by bedtime I was playing the Negro National Anthem ['Lift Every Voice and Sing'], albeit with two fingers," he recalls. "I just loved what I could do with that thing."

After two weeks of lessons that began when he was 15, Malachi took a job as pianist at the Atlantic Beer Gardens, a jazz joint located at 14th and U streets NW. The year: 1936. Malachi was a student at Armstrong High School and playing jazz from 9 p.m. to 2 a.m., seven days a week. His salary was $48 a month, $13 more than his father earned as a laborer.

At age 16, he was hired away to work at the Jungle Inn, another nightclub located at 1200 U St. Jelly Roll Morton was the manager of this club and during intermission between "top name" acts, Malachi played piano while an up-and-comer named Pearl Bailey sang and danced.

Those were Jelly Roll's last days, spent right here in the city, and when he died, Malachi packed up and hit the road to work with the likes of Charlie Parker, Dizzy Gillespie, Miles Davis, Dexter Gordon and Sonny Stitt.

Now here he is, back in town and playing as smooth as ever.

"Success means different things to different people and I feel I have been successful in my associations and in my love for the piano," Malachi says. "It's a very personal thing. I didn't start out to be a piano player. I was just blessed with good luck."

It wasn't luck that caused Peter Sellars, director of the American National Theater at the Kennedy Center, to call Malachi to play the part of a hotel lounge pianist in the upcoming play, which is about pre-World War II Italy. The play calls for a range of music from "Giovinezza," the Fascist national anthem, to a Fats Waller style of piano playing.

Of course, the night before there is Malachi's concert at the Ellington School, with Charlie Parker bebop as its theme, updated into Malachi's inimitable 1980s style.

"When you love what you do, you can do it anyway you want," Malachi says with obvious pride in his versatility. "A tailor may specialize in making pants, but if he doesn't know how to cut a suit, he ain't much of a tailor."