The concert-after-the-concert, from 11 p.m. Tuesday until 6:30 yesterday morning in the Kennedy Center Concert Hall was Virgil Fox, practicing for a May 6 performance that will be slightly shorter than his rehearsal.

Fox is planning to play 19 works of Bach then, on organ and harpsicord to commemorate his 50th anniversary as a concert musician. The program will hardly allow him time for his verbal musical-spiritual pitch.

"I'm just going to say, 'We are starting where all strings are tuned - A - and we are going to go up an octave has ever lived," he said.

"The Bach Gamut," as he calls it, will consist of toccatas and fugues in "every key on the keyboard except F minor, " and will "gradually pull the audience up until you have arrived at the zenith," Fox promised. "And I'm the cookie who dreamed it up.

"In this life, we need to be pulled up - up to where there's no pollution, up to where the sunlight originates, up to where the air is clear."

Fox who lived briefly but spectacularly in Hammond Castle in Gloucester, Mass., is now based - the two or three months of the year when he is not traveling - in Palm Beach, Fla., where he has "a pink villa on the edge of a hill, 150 steps from the ocean, with 18 feet of the Atlantic Coast."

When he broke with the other trustees of Hammond Castle, who were local residents, they didn't know what he had been planning for them - "a Bach picnic, with 10,000 kids." The 1920s medieval castle was to have become a Virgil Fox Center for the Performing Arts, but the local trutees "had no understanding whatsoever of my program, and my image which made the whole thing possible," Fox said.

"Every human being in his life probably makes one mistake, and mine was not to get control there. I was the entire affair - it was my money, but the minute they saw warm bodies coming through there (as tourists) during the summer for about six weeks, they said, "Who needs Virgil Fox?"

A lawsuit which was settled out of court got Fox back some of his investment, and he is having his own organ installed in the 50-feet music room of his new house designed by Addison Mizner.

"Living in Palm Beach is like living in paradise," he said.