A University of Maryland professor was indicted yesterday on felony charges after his daughter told authorities she was sexually abused by him over a period of 16 years, from third grade through graduate school.

Frank J. Munno, who heads the university's nuclear engineering program at College Park, was charged by a Prince George's County grand jury with four sex crimes, including incest and child abuse, which is punishable by up to 15 years in state prison.

"I've learned it's sometimes easier to explain what happened than to keep it a dark secret," said Angela Mattson, 28. Most who allege incest and sexual abuse do not want to be identified, or tell their stories publicly. But Mattson said she wanted her name used in this story.

"It's something that happened to me," said Mattson, who lives in Bowie with her husband and works as an engineer for the Nuclear Regulatory Commission. "It's part of me. I'm 5-foot-3, I have light brown hair, I was a victim of incest."

Munno, 54, a tenured, $89,000 a year professor who has been at College Park for 32 years, denied his daughter's allegations.

"I plead not guilty," he said by telephone from the house he shares with his wife, Angela's mother, about a half-mile from the College Park campus. "That's all I can say. I plead not guilty. I can't answer any questions."

Describing years of what she called manipulation by her father, and its emotional effects on her, Mattson said that in the early 1980s she considered suicide.

"But I felt like this was my lot in life, and it had to be happening for a reason," she said. "And the only reason I could come up with was to keep this from happening to someone else. And that's why I'm here now . . . .

"What I'm hoping," she said, "is that there's a potential abuser out there who's going to see this and realize that his daughter's going to grow up to do something, press charges.

"And maybe he won't go into her bedroom."

Munno, who also has two grown sons, joined the College Park faculty as an assistant professor in 1958, received a doctorate in nuclear engineering six years later and became a full professor in 1973.

His department chairman, professor Marvin Rouch, said he was shocked by the charges and described Munno as "a very caring person, certainly one who worked very hard on behalf of his students . . . . I don't know that he could be described as nationally eminent, but he's extremely eminent on campus."

The university had little comment on the indictment.

"At this moment, we have no information upon which to react to this situation," spokeswoman Roz Hiebert said in a statement.

"When we receive the appropriate facts, we will assess the situation carefully."

Gary Melton, a professor of psychology and law at the University of Nebraska and a member of the U.S. Advisory Board on Child Abuse, said it is difficult to determine accurately the prevalence of incest in American society.

He said studies show that as many as 5 percent of boys and 15 percent of girls are abused at some point during their childhoods, most commonly by someone they know well.

The figures for incest would be somewhat lower, he said.

However, Melton said, it is clear that a greater awareness of the problem has resulted in more reported cases in the last decade.

"It is only relatively recently that people have acknowledged that {the problem of incest} really existed," Melton said.

Prosecutors said Munno will be mailed a summons to appear for arraignment in Circuit Court. Besides incest and child abuse, he was charged with unlawful carnal knowledge and unnatural and perverted sex practices.

The indictment covered a range of offenses that allegedly occurred between 1969 and 1987.

Mattson said the first alleged incident left her "terribly confused."

"After a while, it was very clear that this was the way I could show Dad that I loved him," she said.

"There was not a lot going on that I understood," she said. "And somehow I felt that I was less worthwhile than everyone else. Looking back, I think I felt inside me that I had to earn my daddy's love -- whereas other people, their daddies just loved them no matter what they did . . . . "

Fearing a loss of her father's love, Mattson said, she did not resist him.

As a teenager, she said, "my bed was against a wall, and very often I would bury my leg between the bed and the wall to make myself less accessible. But I knew that when he'd come into the bedroom, I couldn't stay like that, because that would turn him away. And I couldn't do that."

Mattson said she could not bring herself to tell her mother or brothers about the alleged episodes. Her relationship with her father, meanwhile, discouraged her from making friends, especially with boys, she said.

"And through the years, I'd hurt other people a lot because I didn't want to hurt my dad," she recalled. "I would not date out in the open. I would see guys on the side. And if it got to a point where I thought my dad might find out about it, I'd stop it cold . . . . I'd just make up an excuse."

She enrolled at College Park in 1979 as a nuclear engineering major. Six years later, as she worked toward a master's degree in the field, she said, her father acted as her thesis adviser.

"The first years of college is when I went through promiscuity," she recalled. "If a guy found me attractive, I'd just feel, 'Wow! Someone thinks I'm attractive!' And if they didn't mind my dad not knowing about us, I didn't mind going to their apartments instead of going to math class . . . .

"And I began realizing that I was not going to have a loving relationship with anyone," she said, "because I couldn't date out in the open."

It was that realization that prompted her to consider suicide, she said.

In March 1987, finished with graduate school and working at the Defense Nuclear Agency in Bethesda, Angela Munno started a romance with Philip Mattson, an Army major whose marriage was failing. That July, as they traveled to Southern California together on business, she said, she shared her secret.

"I was just devastated," Philip Mattson recalled.

For the rest of that summer, he said, he read anything he could find on incest, and pleaded with Angela to seek professional help. In October, she said, she attended a meeting of Survivors of Incest Anonymous.

"I saw that it happened to other people," she said. "And they had the same kinds of feelings that I did. That amazed me, to hear other people saying the same things I was. It was powerful, to know I wasn't alone . . . .

"They pointed out the manipulations they went through, and I'm hearing them talk about what their fathers told them," she said. "I'm thinking, 'You bought that?' But it was the same thing I bought. I was able to see this stuff from an outside perspective, and it started to become clear."

She moved from her father's home to a Silver Spring apartment two months later, in December 1987. But she learned that the move, and her weekly sessions with the support group, would not be enough, she said.

"I was going through a lot of emotional difficulties in coping with what I'd just done to my dad by leaving," she said. "Did Daddy still love me? There'd be times at work when I'd just start to cry, and I didn't know why. I'd hide in my office. And there were days I was afraid to get up out of bed."

So she started therapy, and continues today, two sessions a week, one of them private, one with a group. She married Philip Mattson a year ago. "I've learned that I'm not worthless," she said. "What happened, happened because of how much I loved my father, and how much I wanted him to love me. I didn't want him to not love me, so I never said no."