A Falls Church man being sought by Fairfax County police in a child sex-abuse case apparently killed himself the day after police searched his apartment and uncovered what they said was one of the largest collections of child pornography ever seized in Virginia.

On Wednesday, county police searched the apartment of Liston H. Whiteside, 43, at 7629 Matera St. in Falls Church; Thursday his body was found in Catoctin Mountain Park near the presidential retreat of Camp David in northern Maryland, with a bullet wound in the head, according to Maryland State Police, who said the death was a suicide.

The material found at Whiteside's two-bedroom apartment included 85 pornographic books; seven 8mm films involving acts of pedophilia, including a movie titled "Little Ones in Love;" numerous cardboard boxes containing about 360 photographs of nude children, some pictured with Whiteside, and cameras, tape splicers and cutters and other materials used to make and process 8mm movies, according to an inventory filed in Fairfax County Circuit Court.

"This is one of the largest seizures we've had in recent memory," police spokesman Warren R. Carmichael said.

Whiteside, a management analyst with the Naval Supplies Systems Command in Crystal City, was aware that a search warrant had been executed at his home, according to Carmichael.

More than 10 Maryland state troopers searched the wooded area near Camp David for nearly five hours on Thursday in an attempt to find and arrest Whiteside on a charge of statutory rape.

Fairfax authorities said Maryland police had been alerted that Whiteside was depressed, possibly armed and had threatened to commit suicide. His car was spotted by the side of the road and his body, with an apparently self-inflicted shotgun wound in the head, was found by a bloodhound at about 7:45 p.m., according to Maryland State Trooper William T. Presgraves.

"Although society probably figures that we're all better off when these guys do commit suicide, I feel that it makes it worse for the children," said Fairfax County Assistant Commonwealth's Attorney Corrine J. Magee, who was assigned to the case. "It makes the child feel somewhat responsible for it because victims often develop a friendship relationship with the pedophile."

Carmichael said the investigation began after police received information from the Fairfax County Department of Social Services regarding what they believed was a sex-abuse case involving a juvenile.

He said police officers, headed by investigator Daniel W. Gollhardt, interviewed the child and obtained a warrant to search Whiteside's apartment on the basis of information obtained from the alleged victim.

From the photos seized in Whiteside's apartment, five female victims of sex abuse between the ages of 11 and 15 have been identified by police, according to Magee, who said that four of them were Fairfax residents.

"It is seldom we get something this large, although we know it's out there," said Magee.

"Even though it will cause embarrassment, we will be attempting to notify the families of the other victims to make sure they can avail themselves of counseling so that they don't have to live with the secret," Magee said.

Gollhardt, who has been qualified as an expert in cases involving child abuse in Fairfax County Circuit Court, said in an affidavit in support of a search warrant that the sexual activity that occurred was oral sodomy, a felony in Virginia.

According to the affidavit, Whiteside took a large number of photographs of the child first identified by the social services department and himself involved in sexual activity, and the photographs were kept in Whiteside's bedroom.

Under state law, it is a felony to possess, produce or make sexually explicit visual material that uses or has as a subject a person younger than 18.

An employe of the Idylwood Village West Apartments, where Whiteside lived, said yesterday that she was "shocked" to hear of the allegations against him. "He was a very, very nice man," she said, and he paid his rent on time. There had been no complaints from tenants about him, she said.

Whiteside, described as about 5-foot-7 with a small frame and thinning sandy-blond hair, seemed to be happy and had remarried in June, she said. Whiteside told her that he and his new wife planned to move to Maryland.

"About a year ago, we had a problem with someone knocking down a barricade on the property, and he told me he had called the police," she said. "He was a model tenant."

Investigator Gollhardt, assigned to the county's Criminal Investigations Bureau for the past eight years, said in the affidavit that offenders who sexually abuse children often photograph the children during sexual activity and that they often collect pornographic matter, magazines and books and keep accurate records of the sexual activity. They rarely dispose of those records, according to the affidavit. ITEMS SEIZED BY POLICE

Among the items seized from Liston H. Whiteside's Falls Church apartment, according to a search inventory, were:

*A Polaroid camera.

*A Super-8 movie editor.

*A suitcase with photo-processing equipment.

*A Zenza Bronica camera.

*A cardboard box containing 85 books showing children and adults engaged in sex.

*104 pages of photocopied photographs of juveniles, male and female, in sexual poses.

*A small cardboard box containing 103 Polaroid photographs of a child and Whiteside naked and involved in sexual activity.

*A cardboard box containing 155 Polaroid photographs of naked children involved in sexual poses and sodomy offenses.

*13 books of naked children by David Hamilton.

*An 8mm movie with children titled "Little Ones in Love."