She's a delicately featured 9-year-old with long blond bangs and bright blue eyes, but she doesn't act like most girls her age. She seldom plays outdoors and never alone.

Her parents say she's distant, tumbling through a laughless childhood derailed almost two years ago. "My daughter was raped by a juvenile who was a very good, close friend of ours," her mother recently told the Senate's Juvenile Justice subcommittee.

The girl also testified in the glare of television lights and before sympathetic onlookers in the crowded conference room. Her words were clear, her voice strong, her Cabbage Patch doll by her side. Yet, a friend of the family remarked: "She will never be the same. She lost her childhood. It's gone."

Her 13-year-old baby sitter, who is now almost 16, was charged with raping and assaulting her when she was 7.

"He's a rat," she said recently.

The teen-ager was convicted on the rape charge, but the conviction was set aside because an error by the judge was held to have denied him a fair trial. Today he is free and maintains through his lawyer that he is innocent and that someone else is the culprit. Now an appeals court must decide whether he can be retried.

Her family has since moved to another area in suburban Washington. And both she and her mother are undergoing therapy at a sexual assault center.

"It's a twisted mess," her mother says. "I'm scared for my daughter. My God, she's just a baby. How is she going to realize that sex is a beautiful thing? How is all of this going to affect her?"

In the Washington area, as in the rest of the country, sexual abuse of children has come crashing out of the closet: Sen. Paula Hawkins (R-Fla.) reveals that she was sexually molested at the age of 5; "Something About Amelia," a story of incest unnerves a national television audience of more than 60 million; six people who work in a Manhattan Beach, Calif., preschool center face 115 counts of child molestation.

Suddenly, a topic too shameful even to talk about is being closely examined over morning coffee in newspapers, in magazines, on talk shows and at professional conferences.

And for the Washington area and its more than 800,000 children, the problem of sexual abuse is becoming all too real.

"I think that if child molestation was a disease it would be an epidemic," said Stephen R. Mathews, a 15-year veteran with the D.C. Police Sex Offense Branch. "If it was something that gave every child . . . a rash on his forehead, we would really be surprised by the magnitude of the problem here ."

In the first quarter of this year, half of the sexual assaults reported to District police involved child victims, a 39 percent increase in two years, police said. The increase in new cases has been so dramatic that the D.C. Police Department sex branch is creating a special sex squad to deal with children.

In 1982, the Sexual Assault Center at Prince George's County Hospital had 290 cases of sexual child-abuse. Last year, the number of cases climbed to 363, a 25.2 percent increase.

Paulette Jackson, a social worker for Alexandria's Child Protection Services, says "there has been a sharp increase here." She says her colleagues are developing a team concept--already in use in Arlington, Fairfax and the District--to treat young victims of sexual abuse and their families.

The team concept involves coordinating pediatricians, psychologists, social workers, nurses and psychiatrists in the care of the victim's immediate and long-term medical and emotional needs.

At Children's Hospital in the District, "we are seeing . . . over 400 new incidents each year," said Joyce Thomas, director of the hospital's child protection division, which has handled more than 2,000 Washington-area cases since the unit opened in 1978.

"After focusing on child abuse, we became more aware that not only were children being beaten, they were also being raped, and raped in a different way," Thomas said, explaining how the program started. "Some were being physically, violently raped. Others were being manipulated, bribed and coerced to participate in acts that have long-lasting, severe implications to their health and their ability to grow in a normal way."

Thomas said sexual abuse of children, a problem as old as humanity, only began to be widely recognized as a special problem--apart from other types of child abuse--about a decade ago. But experts caution parents not to begin imagining a "ghost around every corner."

A report released recently by the National Association of Social Workers estimated that one in eight females in the United States will be a victim of sexual abuse before the age of 18.

But no one seems quite sure whether the number of sexual-abuse cases is up, or whether the reporting of such cases has increased.

Some speculate that there has been an increase in the number of cases, specifically because molesters feel less inhibited, encouraged by a more permissive society.

Others say recent media attention has made people more aware of the problem, which has led to more reports of sexual abuse of children to authorities.

"The problem has probably always been pervasive," said Sheryl Brissett-Chapman, clinical services coordinator for the child sex-abuse team at Children's Hospital. "I think children are saying I have a problem, and adults are ready to hear it now."

Yet, area specialists said they believe that less than 10 percent of the cases involving the sexual abuse of children are ever reported. "I don't like to go to cocktail parties and say what I do," said Brissett-Chapman, "because you will get someone who will say 'I never told anyone before, but when I was a kid I was sexually abused.' "

Mathews and other experts speculate that the risk of becoming a sexual-abuse victim is higher for Washington-area children than for those in other parts of the country. Demographics suggest that the Washington-area population is shifting from child-centered to career-driven families.

In the District, there is a growing number of families in which both parents work. There also are more female-headed households. District police say they believe both households are more vulnerable to molesters who quickly identify unsupervised "latchkey kids."

The 1980 U.S. Census reports that of the District's 63,403 families with children under 18, almost 30,000 live in single-parent households that are usually more dependent upon day-care facilities and baby sitters than traditional nuclear families. It's a dependency, D.C. police say, that increases the molester's opportunity to strike.

Police say no community--Chevy Chase, Anacostia, Capitol Hill, Rosslyn or Old Town Alexandria, for example--is immune from child molestation. They say a child's sex, race or family is of little consequence to the molester.

The victims, usually female, are sometimes infants, but the average age is about 8 years old, says Thomas of Children's Hospital.

The molester can come from within the family, as in incest, or from the outside, but more often is someone the child knows, police said.

National studies show that in as many as 85 percent of all cases of child molestation, the child knows the offender. And local police say that in almost half of those cases the molester is related to the victim.

"The one thing this offender isn't is a hunchback lurking in the dark," says the commander of the D.C. Sex Branch, Capt. John Collins, who is trying to dispel a popular "stranger danger" notion that child molesters are easily identifiable figures children can be taught to avoid.

"They are pedophiles," he says, describing people who prefer children as sexual objects. "They can be teachers, lawyers, policemen and child advocates and come dressed in three-piece suits."

Unlike the rapist who earlier this year stalked children in Southeast Washington's Congress Heights neighborhood, the pedophile tends to seduce his victims by first becoming their friends, says Mathews. They usually begin sexual relations gradually, he says, and may sustain them for years, leaving the child with few physical indications of molestation.

And police say the pedophile's age varies. "We've come in contact with them 30 up to 70," says Detective Wendy Alexander of the Prince George's County Police Department. "It's been our experience that most of them develop a preference for sex with children at an early age but aren't usually caught until middle age."

Pedophiles are almost exclusively male, says Collins. They often work or volunteer in activities that bring them in contact with children, such as schools, scouting groups and day-care centers, according to D.C. police.

And the pedophile is organizing.

The FBI says the Pedophile Information Exchange, the North American Man Boy Love Association, the Children Sensual Circle and the Rene Guyon Society, which has the motto "Sex by Eight or It's Too Late," have been identified nationwide. Police say they do not believe any of the groups operates in the Washington area.

The pedophile's driving force is the sexual conquest of children.

"He works on the child's curiosity, [his or her] need for love, attention and affection," says Mathews. "He provides the attention that the child craves. He also fills an attention void left by the parents. In fact, once the pedophile has the child in his trust, the child will look more to him than to his parents for advice and affection."

"He or she is usually an intelligent person," Mathews says. "He is not ignorant, and he is very, very deceptive."

The pedophile often attempts to erode the child's resistance to his advances by using drugs, money, gifts and treats such as trips to movies and amusement parks, says Mathews, who is recognized by the FBI as an authority on pedophilia. Sometimes photographs of nude victims are shown to prospective victims to lower their inhibitions, he says.

And once the pedophile gets what he wants from the child, ranging from fondling and intercourse to anal and oral sodomy, authorities say the child often becomes entangled in conflicting emotions.

"You really don't like it and can't stop it," said Ingrid Horton who says she was a victim of sexual abuse from age 10 to 15. "You feel really dirty, and utterly, utterly powerless."

Horton, president of the District's chapter of Society's League Against Molestation, a volunteer organization that counsels victims and their parents and lobbies for tougher laws, warned that there is even a darker side to the pedophile.

"If he feels threatened," she says, "he will sometimes harm or kill his victim to cover his tracks."

But most pedophiles do not kill their victims, says Mathews. Rather, they thrive on sexual conquests, and often photograph their victims, he says.

An ordinary-looking photo album marked "EVIDENCE" sits atop a detective's desk at the District's sex branch. Inside are the color photographs of more than 100 of the area's male children, one page for each victim. All are minors aged 11 to 16, all are nude and all are photographed in sexually suggestive positions.

District police say the youths in the photographs are victims of a Northwest Washington man who worked in an area "child-oriented program."

The man, who has pleaded guilty to multiple charges of sexual molestation, has not yet been sentenced.

D.C. Superior Court files are crammed with stories of sexual abuse of children: A 5-year-old Northwest Washington girl contracts gonorrhea when her father rapes her; a 25-year-old man corners a Southeast Washington girl in her home and orders her to wear high heels and stuff her blouse so she appears pregnant before he attempts to rape her; in Northeast Washington a 6-year-old girl tells people how her uncle kisses and touches her.

"I think every circumstance that you've heard about or read about in the papers that's happening all over the United States has happened right here in the metropolitan area," Mathews says.

"I want people to know what happened to her so it won't happen to other little girls," says the Washington-area mother who testified before a congressional committee in behalf of her daughter.

Months before she would learn of her daughter's revelations, she said she had become disturbed by her daughter's seemingly sudden illnesses.

"I would get a call from the school nurse to come get her. When I got to school she told me she was complaining about stomach pains," she said earlier at her home.

Despite numerous visits to private physicians, a problem could not be found. When her daughter complained of burning in her genitals, a urologist cautioned her not to permit the child to take bubble baths.

She said her daughter began to do very poorly in school and was always tired.

"She looked dirty and sloppy," her mother said.

Then one day, according to the mother, a friend of her son's told her to ask her daughter what had been happening.

"I went cold all over. I called [her] and asked her what had [happened]," she said.

Over the course of an evening, the mother said, her daughter told her story. "I was hysterical," she said. "Why would anyone pick on a 7-year-old baby? Why would anyone pick on a baby that knows nothing about the facts of life?"

"She said it hurt so bad she would try to close her eyes and go to sleep," she said.

" She doesn't want to be with anybody," her mother said, her voice cracking. "She wants to be alone. She's scared. She'll always be scared."