Whizzing out of the children's ranks and the roller rinks and onto the disco stage and the mobbed urban sidewalks, roller-skating has come of age.

The Rollerskate Company (244-0869), a sort of roving roller skate store, is selling and renting skates, giving lessons and conducting skating excursions for party entertainment. Partners Donna Fry and Al Edwards stake out the corners of 15th Street and Constituion Avenue NW on Saturdays and Calvert Street and Connecticut Avenue NW on Sundays (11 a.m. to 7 p.m., weather permitting) to rent skates ( $3 the first hour, $2 thereafter; collateral is a driver's license and credit card or $25, or you can join a supervised skating tour) to adverturers who want to take a whirl around the Monument or through Rock Creek Park. They've also ventured into the disco circuit, renting saktes and demonstrating steps at L.A. Cafe and Foxtrappe. For $70, they'll sell your own pair of city skates (shown above). Called Sure-Grip Joggers, they're jogging shoes with indoor/outdoor wheels.

SweetSkates, in summer retreat now at its store in Rehoboth, Del. (8 N. 2nd St., 302/227-2012), operates a skating concession at 20th and P Streets NW (daily, probably from 7 a.m. to 10 p.m., but check by calling 585-3683). For $2 an hour or $8 a day (collateral is $25 and an I.D.) you can rent a pair of high- or low-top SweetSkates fitted with versatile polyurethane wheels (selling for $105 to $135). For $1 an hour extra, you can rent protection, too (helmet, elbow pads, knee pads and gloves). Owners Sam Talbertt and Sandy Dezen have also come up with a new form of party entertainment called a Disco Revue - four disco dancing pros, for hire, go through their routine on skates. CAPTION: Picture, no caption, by Bill Snead