Twenty years ago this week, incomparable Glenna Collett Vare won her sixth United States championship, a feat unparalleled before or since. On the 34th hole at Minneapolis' Interlachen Country Club, Mrs. Vare, 32, defeated 17-year-old newcomer Patty Berg, 3 and 2. Her women's U.S. Amateur victories spanned 13 years. The champion, who said motherhood improved her game, still plays a few tournaments after two children and 38 golfing years. Her son, Ned, now heads the Yale golf team.