Carol Hasegawa of Washington penalized herself out of a victory in the Keefer Cup yesterday at Chevy Chase and eventually lost a playoff to Sue Keeney of ArmySNavy on third extra hole.

Hasegawa, a 14-handicapped golfer, could have won the 46th renewal of this tournament by a stroke, but called a penalty on herself on the 12th hole when the ball moved as she was addressing it. That gave her a five instead of a four on the hole and a net of 144 for the 36-hole event, placing her in a tie with Sharon Briggs of Montgomery Village and Keeney.

Briggs was eliminated on the first extra hole with a double bogey. Keeney, a former District champion who has a two handicap, parred the hole but had to give up a stroke to Hasegawa, who had a five.

Hasegawa had a chance to win on the second hole but missed a three-foot putt. Hasegawa hit a tree on her second shot on the third extra hole, was short on her third shot, caught the trap on her fourth and took a double-bogey seven. Keeney was on in two and, from 20 feet away, lagged the ball for three putts and her victory.

Keeney had another 74 yesterday to go with Wednesday's score for a low gross of 148. But since this is a net tournament, Keeney took the Keefer Cup. Last year's champion, Rebecca Doman of Argyle, won low gross with 162, coming back with a 78 yesterday after an opening 84.

Keeney had a pair of 37s yesterday, hitting 12 greens. She had two birdies and there bogeys on the front. She parred the first three holes on the second nine and then bogeyed the 13th and 14th when she three-putted. She then parred in.

Hasegawa, a newcomer to Division I team play this year, broke 80 for the first time in her golfing life, coming in with a 79 to go with her opening score of 93. Nancy Hollenbeck, who had a 78 Wednesday, slipped to an 89 yesterday.