Next weekend will offer several opportunities for supporting some of the younger jazz musicians in Washington; in two cases, it will be one of the last opportunities, at least for awhile. Twenty-one-year-old drummer Winard Harper, who has played many of the city's clubs and worked with many of the area's top jazz musicians during his three years here, and his brother, 18-year-old trumpeter Phillip, will leave Washington at month's end for the University of Hartford, where they will be under the wing of famed saxophonist Jackie McLean, who is a professor there.

Both brothers took up their instruments early. Phillip has been blowing his horn for eight or nine years while Winard began on the drums as a precocious 5-year-old after his older brother caught him banging on tin cans with pencils. The Harpers will take the D.C. Jazz Quintet into the One Step Down Friday and Saturday. Roger Woods will be on alto saxophone, Larry Scott at the piano and Pepe Gonzalez on base.

Woods, who will enroll at Hartford next spring, also will take part Saturday in a Charlin Jazz Society summer youth interns program at George Washington University's Marvin Theater. The evening will open with dancers, singers and comics from the Duke Ellington School for the Arts and continue with New Faces Jazz, a showcase for some of Washington's most impressive young talent.

Other performers will include Keith Holmes on trumpet and flugelhorn, baritone saxophonist Charlie Young, guitarist Paul Bollenbeck and vocalist Jamie Broumas. Rhythm will be provided by veteran players John Malachi at the piano, bassist Keter Betts and Nasser Abbadey on drums.