Music: Grand Slam on the Grand

When he won the Leventritt Award last fall, Pianist Malcolm Frager, 24, was hailed as one of the most promising keyboard talents to turn up in many a year. The son of a St. Louis stocking manufacturer, Frager started playing the piano at four, was giving recitals when he was six, has appeared with most front-rank U.S. orchestras. Last week, against a field of twelve finalists, Frager walked off with the $3,000 first prize in Belgium's Queen Elisabeth Concours, becoming the first instrumentalist to win the two toughest competitions in music.