Medalist Amy Geithner of Fairfax used her superiority on the greens to defeat Angie Munno of Argyle, 3 and 1, yesterday in the quarterfinals of the Women's District Golf Association championships at Lakewood.

In other second-round matches, Sharon Briggs of Montgomery Village was too strong for Shawn McCullough of Tantallon, 5 and 4; Kim Williams of Bethesda held off Fran Schultz of Army Navy, 2 and 1, and 1978 WDGA finalist Diane Rankin of Montgomery Village eliminated Lorraine Elder of Army Navy, 2 and 1.

This morning's semifinals show Geithner versus Rankin at 9:36 a.m. followed by Briggs versus Williams at 9:42.

Geithner, a 22-year-old graduate student at the University of Maryland, three-putted the second hole but took only one putt on each of the next four holes for a 2-up lead.

Munno, a senior engineering student at Maryland, came within one hole with a par at the seventh hole. She appeared ready to even the match when she hit her approach shot three feet from the cup on the par-5 eighth hole, but earned only a tying birdie when Geithner dropped in a 20-foot putt.

After both parred the ninth hole, Munno was again frustrated at the par-5 10th. She hit the stick with her 40-yard third shot and her ball stopped four feet from the hole. But after Geithner two-putted from 50 feet for par, Munno missed her short putt and remained one hole down.

Geithner regained a 2-up lead at the par-3 12th, when Munno three-putted from 50 feet, and halved the next hole in bogey when Munno again three-putted. Geithner ended the match with par at the 17th.