ANYONE WHO has ever attended a class or performance at the Dance Place's Adams Morgan studio has had to pass through the alley that runs between 18th Street and Columbia Road. It isn't the most inviting spot on the planet: The ground is often littered, the trees overgrown, the signposts minimal and crude.

All that changes this weekend, when the passageway officially becomes Dance Alley. Street signs have been installed, the trees have been trimmed and a neighborhood youth group, the Ontario Lakers, has waged a clean- up campaign.

This Friday at 6:30, a dedication and ribbon- cutting ceremony will take place in the center of the alley. And most likely, Carl Jackson, aka Mr. Rhythm, will sanctify the pavement with a round of the "shim sham" -- the tap dancer's national anthem.

The ceremony will be followed by back-to- back benefit performances by the nine- member music ensemble Mamaya. Led by Senegalese artist Djimo Kuyate, the group produces a rousing brand of contemporary African sound geared specifically to dancing. The plan is to transform the Dance Place into a disco for the night.

These celebratory doings come at a time when the Dance Place faces displacement because of a substantial rent increase. The organization's directors are hoping that a big turnout will bolster their cause.

DANCE ALLEY DEDICATION -- Friday at 6:30 p.m., alleyway between 18th Street and Columbia Road NW, followed by Mamaya shows at 8 and 10:30 p.m. The Dance Place is at 2424 18th St. NW. Tickets $10. Call 462-1321.