A 54-year-old Fairfax City man pleaded guilty yesterday in a Fairfax County court to seven charges that he had sexually abused three girls less than 10 years of age on several occasions at his home last summer.

Joseph William Welsh, of the 10600 block of Maple Street, faces up to four terms of life in prison. His sentencing was scheduled for Feb. 1.

According to police testimony, Welsh got to know a 7-year-old girl and her 9-year-old sister from his neighborhood by inviting them to a shed behind his house, where he operated a reupholstery business. There, he took them into his confidence, telling them about his sexual acts with a girlfriend before sexually assaulting both girls.

Later in the summer, Welsh sexually assaulted an 8-year-old girl whom he met through the older sister, police said.

The girls visited Welsh about seven times in all, police said, and kept the visits secret until the 8-year-old girl confided in her mother in early October.

The girls' parents said after the trial that they were satisfied with the plea, but expressed concern that Welsh would someday go free.

"In a number of years, no matter how many life terms he gets, he's going to come up for parole. So my biggest thing now is to know when that is, so I can write my little letters" protesting any parole, said the mother of the 8-year-old girl.

The mother said she never gave much thought to Welsh, knowing him primarily as a resident of the neighborhood whom the family dog did not like, and whose trash was considered gold by her daughter and her friends. "He's constantly throwing out nifty things, like broken chairs," she said.

Now, in retrospect, she thinks she remembers the day her daughter was assaulted. "After that, she got real moody. Little things would totally set her off."

It took months for the story to come out. At first, the daughter hinted that something bad may have happened to the two other little girls, said the mother. "My daughter made mention of it, but I didn't believe her," she said. "I believe now it was her way of testing me to see if I could handle it . . . . My daughter is very protective of me."

The mother coaxed the daughter to tell her what had happened after she overheard the girl telling a friend that she had a secret to tell.

"I figured she'd thrown a rock through a window at school or something. I figured it was school-related," she said. The truth, she said, "was like a brick wall at 50 miles per hour came and slapped me in the face."What people do not want to think about is that maybe their best friend molested a child," she said. "They want to believe their judgment of people is excellent and their gut feeling is right. It's just not that way."

The parents of the other two girls said that the sisters were too ashamed to tell them about the incidents "because we always preach about not talking to strangers," their stepfather said.

"I blame myself in part because I should have gone outside with them" while they played, said the two girls' mother. "At the same time, you cannot keep your eyes on the kids all the time. I feel very helpless."