SELDEN, N.Y. (AP) _ Classmates sometimes saw black-and-blue marks on Cheryl Pierson's body, but she told them they were nothing to worry about.

Now authorities say those bruises were the only indication that the 16- year-old cheerleader had suffered five years of incestuous abuse at the hands of her father.

The situation didn't come out into the open until her father, 42-year-old James Pierson, was shot dead in the family driveway. Miss Pierson and her boyfriend were arrested and accused of paying a 17-year-old schoolmate $400 to kill him. Miss Pierson and the schoolmate were charged with the death; the boyfriend with conspiracy.

''If a kid comes into school and is banged up, I would think it would come to somebody's attention,'' said John G. Ehrlich, chief of the family crime bureau of the Suffolk County district attorney's office.

But Miss Pierson had never been mentioned in any complaint to his office. Ehrlich's staff has increased from two to six in the past four years, while the number of child abuse complaints increased tenfold.

Work in recent years to uncover cases of child abuse ''makes this all the more troubling. There is an avenue. They don't have to kill their father,'' said Arthur Dermer, principal at the school Miss Pierson attended, Newfield High School in Coram.

''There were a lot of ways she could have avoided the problems with her father,'' agreed Assistant District Attorney Edward Jablonski.

Miss Pierson's lawyer, Paul Gianelli, said she now realizes there were alternatives, and regrets her father's death: ''She loves her father.''

At the arraignment, Gianelli wiped tears from Miss Pierson's face as she sat with her hands cuffed behind her. He vowed to prove the killing resulted from five years of ''terrible, terrible abuses'' that culminated a year ago, after her mother's death, when she became her father's ''surrogate wife.''

Police say the destruction of Miss Pierson's home life intensified when her mother got sick several years ago with kidney disease.

Gianelli said Miss Pierson considered leaving home, but remained for the sake of her 8-year-old sister. Then one day she saw her father ''roughhousing'' with her sister and feared that he had found another prey.

According to police, Miss Pierson planned the shooting over several months, and asked friends at school if anyone would kill her father for a fee. Officers say 17-year-old Sean Pica agreed, and Miss Pierson's boyfriend, Robert Cuccio, 19, paid him $400.

On Feb. 5, as Pierson left his home in this Long Island community to go to his job as an electrician, he was shot five times with a .22-caliber rifle.

Police who interviewed Miss Pierson said they found inconsistencies in her story, and that she confessed eight days later.

Miss Pierson and Pica pleaded innocent to second-degree murder, while Cuccio pleaded innocent to conspiracy. Pica remains in jail in lieu of $100,000 bond; the other two were released on bail. No trial date has been set.

Miss Pierson is now in the custody of her paternal aunt and grandmother.

Since Miss Pierson's arrest, Newfield High School has received letters from across the country, many from victims of child abuse who support her. Gianelli said he received offers from strangers who wanted to help pay her $50,000 bail.

Gianelli said Miss Pierson was threatened by her father and warned to never tell about the incest.

''That is not uncommon that kids take this abuse and don't report it,'' Ehrlich said. ''A lot of kids don't come forward with reports of abuse because they're embarrassed and frightened.''

Pica's attorney and friends said if he killed Pierson, it was out of love for a classmate who was being brutally abused rather than for money.

''Whoever did it did it for passion and not for money,'' said Martin Efman, Pica's lawyer. ''It wasn't just, 'Gee, I need a few extra bucks this week. How can I help you, cut your lawn or shoot your father?'''