A town councilman killed his wife, his 9-year-old daughter and then himself with a shotgun today in their home in this quiet southern Maryland community, apparently because of deepening domestic problems, according to State Police.

Don E. McMahon Jr., a 38-year-old retired Washington fireman, and his wife Anne, 38, were found dead in the kitchen and their daughter, Melisa, was found in the basement recreation room minutes after local police received an anonymous call that there had been a shooting at the home.

Anne McMahon had moved out of the home with her daughter last Friday and was making arrangements to lease an apartment, but she had returned today apparently to pick up some belongings, according to authorities.

The daughter had recently told a little neighbor boy with whom she played that "she was moving uptown with her Mommy and new Daddy," according to the little boy's mother, Jan Russell.

State police said they found a lease agreement for a new apartment in Anne McMahon's purse and that there was a suitcase packed in Melisa's bedroom.

The mother and daughter had driven to the home on Bay Street, less than a mile from the Chesapeake, only about 10 minutes before the shootings occurred, according to police. McMahon left no suicide note and neighbors interviewed by police said they heard neither arguing nor shots from the home at the time of the incident, according to investigators.

McMahon, who retired on disability from the D.C. Fire Department in 1971, according to a spokesman, had grown up in North Beach and he and his family were prominent members of the community, according to several townspeople in the once thriving beach resort. Following in the political footsteps of his father, who was once mayor of the town, McMahon had been elected to the Town Council last year and was also serving as the town's building inspector.

Town Clerk Betty Freesland and North Beach Police Chief James Fender Sr. had both talked to McMahon this morning on town business and said he sounded fine.

"I saw him at 10 a.m. at his home," said Fender. "I took him some photos of a building because of a complaint about a permit violation. He thanked me for bringing them and that was it."

Freesland talked to McMahon about 11 a.m., also on town business, and he told her that he would be stopping by her home later in the day, Freesland recalled tonight.

"He was an easy, mild-mannered man," Freesland said. "He was devoted to his little girl. She would often come with him when he came over, a lovely, precious child."

But about four years ago, McMahon had threatened the little girl with a gun, and also threatened to shoot himself, according to a law enforcement source. "He was going to do himself and her both in. One police officer went to the scene and got the little girl and it quieted down. Then they went on living together."

Neighbor Mike Brandell said that McMahon had "threatened people inside the house before. But it never seemed like he was the sort of person who would do anything like that."

Brandell said that Anne McMahon "was really hard on him McMahon all the time. But he really loved her."

In the last few days, said Brandell, McMahon had seemed "depressed and disgusted. But nobody thought it was going to be any sort of a problem."

McMahon, said one law enforcement official, had a daughter by a previous marriage and when that marriage ended in divorce his wife took the child. "Now his wife was making insinuations that she would take his daughter, and he must have flipped," he said.

Anne McMahon had returned to the home today shortly after 12:30 p.m. in her white Pontiac Transam, according to police. Town residents told police they saw her and Melisa, who waved from the car.

State police said they received a call about the shooting at 12:56 p.m. "We haven't been able to find out who called," said one investigator. "It is possible he $ might have called."

Police reached the home minutes later and found the bodies of the McMahons, all of whom had been shot with a 20-gauge shotgun.