"SOME CALL me Mr. Ra. Others call me Mr. Ree. But you can call me Mr. Mystery," says intergalactic jazzman Sun Ra, introducing himself to another ready-to-travel audience. Ra, who predated New Age and predicted electronic instruments, is an improviser and big band leader, known for the pageantry of his three- and four-hour performances with the musicians in ancient Egyptian/African-circus-Star Trek splendor. He arrives Saturday with his 16-piece Arkestra to take us all on a Magical Mr. Ra tour.

Because of his outlandish look and outspoken whimsicality, and his hard-to-label music, moving from Fletcher Henderson's swing band in the late '40s, to hard bop in the early '50s, to pioneering electronic avant-gardisms in the '60s and '70s, Ra has often been called "ahead of his time."

"I was right on time," he announces. "The rest of the world is just catching up. The world ended 2,000 years ago, and you don't even know it yet."

Ra, who reckons he has been around for 5,000 years, refuses to claim Earth as his home planet, insisting instead that he "arrived" from Saturn. And strangely, no birth certificate exists. Ra's passport says his name is Le Sony'r Ra, but he has also gone by Sonny Lee, Armand Ra and H. Sonne Bhlount. As far as we can determine, he first appeared on this planet in Alabama about 75 years ago, and is now living in a four-story house in Philadelphia he shares with musicians.

"I'm residing in Philadelphia," he says. "Living in Philadelphia is not living." This kind of pronouncement (there's more) doesn't always endear him to Philadelphians. But then, Ra says the whole planet needs work. And he's been sent to do it.

"I always tell my friends I wouldn't be caught dead on this planet -- that's not the real me. I was sent here to change this planet, and I'm gonna do it. I'm in God's impossible projects department."

Even the briefest telephone chat with Ra wheels all over his ever-expanding inner universe, taking in his concept of the Omniverse; the frequency and speed of human vibrations and the earth's revolutions; an unpublished "Book of Informations," which he says contains cures for AIDS and cancer and poverty; the spelling of words (he prefers "werd" to "word," "spirtuel" to "spiritual" for reasons he is only too glad to go into); and incidentally, the symphony he's writing for a Paris orchestra, due later this month.

Ra goes on at such length and in such detail with such stuff that it overwhelms. You start thinking it can't be just sideshow spiel. Maybe it's true . . . at least he must believe it. You certainly can't just dismiss him as a crackpot.

"Music is spirit food, soul food," he says. "It can take you places. So I pick my songs meticulously. I don't want to be singing something that's bad for me and bad for the people. I like 'Over the Rainbow' -- that's a good song -- and 'I Dream Too Much.' They need something beautiful."

Which doesn't mean that these beautiful songs won't include their share of extra-terrestrially inspired chaos.

Ra's just-released A&M album "Purple Night" includes a 10-minute version of Mitchell Paris and Frank Perkins' "Stars Fell on Alabama," featuring Ra's charming sort-of-singing; the standard becomes autobiography, about his arrival on Earth. "Love in Outer Space" features the Arkestra in the guise of a tipsy circus band, now galumphing, now tiptoeing with ridiculous delicacy.

And for the first time on record, you can hear the man speak, as he talks a bit about the upcoming Examination Day, introducing a spacy 20-minute opus called "Of Invisible Them" with a not-quite rap that sounds like Gertrude Stein paraphrasing Descartes:

"Are you so willful you don't know you should be, that you think you are only what others say you are? Yet perhaps you fail to realize, that what you are, you are. And thus so. Thusly, if what you reap is what you so, S-O, what you reap is what you are. Amen, because what you am is what you be, and what you is you am, and what you be you are. If what you are is you so."

"Spell so s-o, not s-o-w," he says. "Very important."

OK, if you say "so," it's so, Mr. Ra.

Ra made his name as an expert improviser, using a big band as his instrument, a difficult feat. "Every night it's a different thing," he says. "And I never play the same thing on the piano, I never know what I'm going to play. And I have to be introduced to the piano. When I come to Washington, they may have an electronic piano, and I may have rehearsed on an acoustic piano; we'll have to get to know each other all over. I'll say 'hello, should I know you?' Some pianos aren't good for jazz and classical, they need to be pounded. I need something delicate, something that talks. The band will have to be ready for anything."

Of course, this type of attitude from a bandleader takes its toll on musicians, even some of Ra's stalwarts, some of whom, like saxmen John Gilmore and Marshall Allen, have been with him for three decades.

"I upset the musicians every night, and they tell me about it," he says proudly, and tells a story about this hotshot new drummer who thought he knew it all. "I said, 'I'm gonna upset him tonight. I'm gonna play something you can't play on the piano,' " Ra recalls.

And sure enough, after that night's show, Ra says, the young drummer came back exhausted and confused after the show and said, "I don't know what you're doing." And Ra told him, "Now you're ready to learn."

Imprisoning such freewheeling improvisations on record might seem beside the point, but Ra says he's got that angle figured, too. He claims his records aren't bound by the usual limits of permanence.

"It's not like other records, it will not sound the same every time. It's spirit music. If you play my records, listen to it by yourself. If somebody else comes in the room, it changes. if that person isn't truly your friend, the music will just get softer so you can barely hear it. If you play it with someone who is your friend, you will be able to hear it."

Kids, try this at home!

SUN RA AND HIS ARKESTRA -- Appearing Saturday at 6 at Freedom Plaza, 14th and Pennsylvania NW, as part of the American Discoveries Festival. Free. Call 202/783-0360.