A 24-year-old father of two small children broke nine years of silence yesterday, testifying in a Montgomery County courtroom that he was sexually abused by a well-known and highly successful football coach in a local youth league.

The man, whose name was withheld to protect his family, said during four hours of testimony that the coach, John Stuart Mackintosh, 51, fondled him during weightlifting practices in the basement of St. Camillus Church in Silver Spring, at the coach's apartment and on a weekend outing in Western Maryland.

The man said the sexual abuse occurred over a 10-month period from late 1981 to 1982.

Mackintosh, charged with one count of child sex abuse, served as athletic director and football coach at St. Camillus School from 1959 to 1983. When arrested last June on the sex abuse charges, Mackintosh was football coach at Pallotti High School in Laurel. Mackintosh, who has denied the charges, gave up his coaching post pending outcome of the trial.

If convicted, Mackintosh could be sentenced to 15 years in prison.

The man, who called Mackintosh "Stu," testified yesterday that he decided to tell authorities about the alleged sex abuses last spring after extensive therapy sessions. "I was having a real hard time," the man said in a dry, straightforward tone. "I felt inhuman. I felt alienated from my own body."

On cross-examination, the man said he had discussed the possibility of filing a damage suit against Mackintosh after the criminal trial. The man said he wanted "to be reimbursed" for the costs of therapy.

As his wife listened in a packed courtroom, the man said he was a backup running back and defensive player on the St. Camillus 110-pound youth football team when he met Mackintosh. The man said he and his older brother, who also has accused Mackintosh of child sexual abuse, became close friends with the coach. "I thought he was the greatest man in the world," the man testified.

The alleged sexual abuse began when he was a 14-year-old high school freshman, he said. All of the alleged incidents occurred either while he was alone with Mackintosh or accompanied by his older brother, the man said.

In the summer of 1982, the man said, he told his parents of the alleged abuse. The man's mother testified yesterday that her husband ordered Mackintosh to stay away from her two sons and told the church pastor about alleged sexual improprieties.

According to the man, the first sexual incident occurred in a cabin at Deep Creek Lake in Maryland at the end of 1981, while he was sleeping in a bed with Mackintosh.

After the 1981 football season, the man testified that Mackintosh fondled him three times a week during weightlifting practices at the church. The man said Mackintosh often invited him to his Silver Spring apartment after the practices. There after a shower, the man said, Mackintosh massaged him and touched him inappropriately.

The man also said Mackintosh took nude photographs of him at the apartment. The man said he knew the sexual abuse was wrong, but that he trusted Mackintosh. The man said he waited nearly 10 years to tell authorities because "I was feeling a tremendous amount of guilt and embarrassment. I didn't want anyone to know about it."