A 51-year-old Montgomery County man was convicted yesterday for the third time of sexually molesting a daughter, apparently closing a drama that tore at his family for 13 years and shocked court observers as it unfolded in three trials since August.

Montgomery County Circuit Court Judge Irma Raker found the Boyds resident guilty of two counts of rape, two counts of incest and one count of unnatural and perverted acts for sexually abusing his eldest daughter, now 27, when she was a teen-ager. He has already been convicted by juries of sexually abusing another grown daughter when she was a child and his 15-year-old daughter. In this trial he waived the right to a jury.

Earlier this year, his middle daughter, now 22, refused to testify against her father and Assistant State's Attorney Barry Hamilton dropped the molestation charges against the man in her case. The man's name is not being used in this story to protect his daughters' identities.

The man, who has begun serving 25 years in the state prison at Jessup on the two previous convictions, maintained during the 1 1/2-day trial, as he had in his two previous trials, that the sexual abuse charges arose from a conspiracy between his four daughters and his wife of 30 years.

"The charges exist but the deed -- the crime -- doesn't," the stout man told Raker yesterday after she had found him guilty. "The only people who know anything about it are the ones who conjured up the crime," he said, in apparent reference to his family.

But his 27-year-old daughter, a petite woman with a soft voice, testified that her father repeatedly forced himself on her sexually and threatened to harm her if she told anyone.

She said in an interview after her father's conviction that she was spurred two years ago to tell authorities about her father because of worries that her 13-year-old sister, who had become "introverted," was also being abused by him.

"That's what I was like when I was 13" and harboring the secret, she said. "It was a conflict between, 'My gosh, do other fathers do this to their daughters?' and 'This is wrong -- I know it is, it says so right in the Bible.' "

Raker set the man's sentencing for July 2. He faces up to two life sentences plus 30 years and a $1,000 fine on the four counts.