Sun Ra has been described as the Spike Jones of jazz -- and hailed as a prophet. Performances of his Intergalactic Cosmo Infinity Arkestra have been compared to Greek drama, medieval miracle plays and the 1930s Cotton Club shows of the Duke Ellington Orchestra. Some jazz critics dismiss Sun Ra as a musical charlatan, but the keyboard-playing leader and arranger has had a devoted following for 30 years.

Some members of the Arkestra reside with Ra in communal living circumstances in Philadelphia and the organization travels to Lagos, Montreaux and other far-flung locations for festivals. "Saturday Night Live" has accommodated them, and they are regulars on the Kool Jazz Festival circuit. The orchestra has made more than 100 albums. Tonight in the Old Post Office Pavilion, Sun Ra and the 20-or-so-member Arkestra, all dressed in lame' garb and pyramid caps, will be the star attraction in a costume ball benefit for WPFW-FM and District Curators, an arts support organization. The theme is Cosmic, and visitors are welcome to come in costume.

"I played with a lot of people who are quite famous now," Ra says, "and then I played with Fletcher Henderson for about a year before he left the planet."

In the next breath, Ra will tell of his extraterrestrial origins. "I belong to the Angel race . . . I never wanted to be a part of planet Earth . . . my music represents the potential future, not the future that is supposed to be, it's a sort of advanced herald of something other than what is, which I call the alter-destiny."