D.C. police said yesterday that they were puzzled by what led a woman to critically wound her husband with a handgun Thursday night, then kill herself with a single shot in the chest.

David A. Scott, 40, and Lynn Ryan Scott, 36, lived in the quiet Palisades neighborhood off MacArthur Boulevard NW. The shooting left neighbors wondering yesterday what brought tragedy to a seemingly happy couple who spent free time decorating their two-story, red-brick house on Watson Street.

According to police, Lynn Scott pulled a gun on her husband during an argument in the den of their house, and shot him several times before he staggered out of the house.

Then Lynn Scott apparently turned the gun on herself and stumbled outside to the front stoop, where she yelled, "David, I love you," before collapsing.

Neighbor Michael Glenn, 47, said he was in his driveway building a go-cart for his 5-year-old son about 9:20 p.m. Thursday when he heard "three or four sharp noises" from the Scott house, one door away.

He looked up and saw David Scott, clad in a bathrobe and bleeding from the torso and arm, stumbling across a neighbor's yard into the street.

"I heard him shouting, 'Help me, Help me. She shot me. I'm dying. Get me to a hospital,' " said Glenn, who drove David Scott to nearby Sibley Hospital.

David Scott was listed in critical condition last night after undergoing surgery early yesterday. Lynn Scott was taken by ambulance to Georgetown University Hospital, where she was pronounced dead at 10:35 p.m.

David Scott works at American Petroleum Institute as director of external liaisons for the oil company lobbying group. Lynn Scott worked at Joseph E. Seagram and Sons Inc. as director of Seagram Action Network, a communications division for employes, retirees and distributors nationwide.

"It's a mystery to everybody. They seemed very happy, very much in love," said Hannah Sistare, a coworker of Lynn Scott.

Sistare said Lynn Scott "was in very good humor" on Thursday as the two worked on a Seagram's newsletter they had planned to complete writing yesterday morning.

Neighbors who gathered in small groups outside their houses yesterday afternoon, spoke solemnly about the couple who had moved into the neighborhood shortly before their wedding in the fall of 1985.

Lynn Scott, who was the daughter of a prominent Toledo family, moved to Washington in 1974 and worked for Gulf Oil Co., until she joined Seagram 18 months ago. David Scott, who has two daughters from a previous marriage, moved from his native Mississippi in 1980 to work for the lobbying group.

"Something must have happened that had to have been tremendously painful for both, but especially for Lynn to have pulled a gun and shot the man she loved and had married, and then to have shot herself," said neighbor Donna Glenn.