More than 150 mourners filled a funeral home chapel beyond capacity yesterday, swallowing sobs and dabbing tears during a brief service for four members of a Fort Washington family who died of carbon monoxide poisoning in a freak accident at their home last week.

Afterward, the visitors filed past the four open caskets of Lydia Hardebeck, 50, and three of her children, Kurt, 26, Linda, 21, and Gary, 20.

The husband and father, Marvin Hardebeck, a State Department employe who was called back from assignment in Grenada after the deaths were discovered, wept with his daughter Karen, 23, the only child to survive the accident.

Prince George's County police said the deadly, odorless gas filled the house after the family car was accidentally left running in the basement-level garage. All the windows in the house, except one in Karen Hardebeck's bedroom, were closed at the time.

Initially police thought Lydia Hardebeck, who was deaf, left the car running, but after questioning the surviving daughter during the weekend, they said they believe it was the eldest son, Kurt, who forgot to turn off the ignition.

According to police, Kurt had parked his car in the driveway, thinking his mother had already parked her car in the garage. When Lydia Hardebeck returned from an errand later Wednesday evening, she asked Kurt to move his car and put her car in the garage. Police said Kurt switched the cars and went into the house to eat, apparently forgetting to turn off the car in the garage. The family was discovered Thursday morning by a friend who came to check on them when telephone calls to the house went unanswered.

After the funeral, Gary M. Miller, a supervisor at a Temple Hills training center for disabled adults, where Linda Hardebeck worked, said she will be sorely missed. "She was very outgoing and very conscientious," he said.

Kurt Hardebeck returned home just a few months ago from a tour in the military.

Yesterday Marvin Hardebeck, a native of Michigan who met his wife Lydia in Germany, said he had made no decisions about what he and his daughter will do. He said he is still in a state of shock. "I don't know if it's really hit me yet."