A Pentagon management analyst shot his wife and three children and then took his own life in the family's split-level waterfront home in the Lake Barcroft community, Fairfax County police said yesterday.

Investigators said they could not explain what led Leonard James Fleeger, a 46-year-old civilian Army employe, to shoot his wife Mary Sue Fleeger, 43, and their three children, Brian, 10; Kimberly, 6, and Susan, 4.

Police based their conclusions on a handgun recovered near Fleeger's body and a short, unsigned note in which they said Fleeger indicated he planned to commit suicide and apologized.

"I'm walking in circles, wracking my brain," said Jeanne Fleeger, a sister-in-law expressing the shock of relatives and friends who groped to explain what they said was an unfathomable turn of events in the lives of a "happy, cheerful and pleasant" suburban Washington family.

"It's like a bad dream," said Jeanne Fleeger. "Nobody can figure out why it happened, and nobody ever will. There was something there that nobody knew."

"They were lovely, lovely people," said Jean Meyer, whose husband often played tennis with Fleeger. "I don't think any of us is ever going to find out what happened in that house."

The same day the shootings took place, Fleeger had played a doubles match at the Barcroft Recreation Center. That day he telephoned his 79-year-old mother Ruth in Pennsylvania to wish her Happy Easter and placed the children on the line to say hello, according to Jeanne Fleeger.

Police said the shootings took place sometime Sunday evening at the Fleegers' house at 3804 Lakeview Ter., a red brick split-level where Mrs. Fleeger had grown up with her parents. Her father, retired Navy Vice Adm. John (Peg Leg) Hoskins, died in the Lakeview Terrace house in 1964.

None of the neighbors interviewed yesterday reported hearing any gunshots. According to authorities, all five members of the family had at least one gunshot wound to the upper body. Fleeger was found sprawled beside his wife in the master bedroom. The wife, and the three children in other bedrooms, were found tucked into their beds.

Priscilla McCandlish, a neighbor and friend who discovered the bodies, said, "I did not see any unusual evidence that says: 'This is the thing that triggered it off.' " McCandlish said she wouldn't speculate on what led to the deaths. "Their private hell should not be for the world to see," she said, adding: "You know it doesn't happen in a vacuum."

The Fleeger bodies were discovered around 8:30 yesterday morning by McCandlish, who had a key to the family's house.

McCandlish said she noticed the Fleegers' bronze van parked in front of the house two hours after the husband, a career civil servant, normally left for work. She became alarmed when another neighbor called to say Mary Sue Fleeger, Brian and Kimberly had not appeared at the school bus stop off Columbia Pike.

McCandlish entered the house, found Duchess, the family dog, alive, and then looked in the master bedroom. She saw what seemed like a strange pattern on the bed linen. It was blood.

"I could see someone in bed with a pillow over their head," McCandlish recalled. "I thought I saw blood and decided no way I'm going any further in." Her husband called the police.

The Fleegers were at least a decade younger than many of their neighbors in Lake Barcroft. They were avid tennis players and fixtures at the community recreation center's summer round of barbecues, potluck suppers and swimming meets. This was Leonard Fleeger's third year as a volunteer soccer coach. "He always found time for that," said neighbor and frequent tennis partner, Alban Zolly.

According to Zolly and others, Fleeger, who was called Jim by friends and family, played several hours of tennis Sunday morning. "Mr. Fleeger came up about 10:15 and watched us for a while," Zolly said. "We played for a few hours. I remember we were talking about each having gained a little weight over the winter. I hit a ball past him and he said something like 'in a month, when I get rid of these 10 pounds, you won't be able to do that.' "

Her neighbors remembered Mary Sue Fleeger as a petite, auburn-haired teen-ager who did babysitting around the neighborhood, eventually moving into the house herself after her parents died. Her colleagues at the law firm of Boothe Prichard and Dudley say Mary Sue Fleeger was quiet, a hard worker, and "very dependable."

Leonard Fleeger, tall, blond-haired, was a native of Smethport, a small town in northwestern Pennsylvania. He came to Washington after a tour in the military and rose through the civil service to become a grade 13 analyst in the Systems Development Division in the Office of the Adjutant General of the Army. He apparently met his wife while in Washington; they were married in the early '70s. "Sue took a long time to make up her mind to marry Jim," neighbor Dottie Bjarnason remembers. ". . . I remember her mother wanted her to hurry up and marry Jim because Mrs. Hoskins liked him so much."

Fairfax police called the shootings the worst murder-suicide in recent memory. In 1980, a street away, a State Department employe shot his wife and then killed himself.

Yesterday there were still Christmas lights strung across the front of the house and two orange "Tot Finder" decals on the house's front window, stickers that local fire departments distribute to help locate children in the event of a fire.

"None of us can begin to comprehend this," said Zolly. "There was nothing at all to indicate this, nothing at all. They were a couple like all of us.

"One of my jobs around here was to landscape the recreation center, get it in shape for spring," Zolly said. "Jim never turned me down once when I asked him for help. He was one of the world's nice guys."