The posters arrived in the mail: "Wanted" was emblazoned in red above the photograph of a man, Rudy Nielsen, who has been charged in a Virginia arrest warrant with child abduction. Another poster featured a photograph of his child, Rudy Nielsen Jr., age 9. The posters, hundreds of them, have been prepared and distributed to schools, stores, post offices, newspapers, television stations and radio stations by Shirley Nielsen, the boy's mother, who had temporary custody of him. She says she has not had any contact with her son since he and his father vanished during the last weekend of August while her son was visiting his father.

While Shirley Nielsen has taken the unusual step of printing the posters asking for information about the whereabouts of her son and his father, her story typifies the difficulties police have in finding these children. It is also a vivid reminder that the problem of parental abduction has not gone away, despite the Parental Abduction Prevention Act of 1980.

"Sooner or later we'll find him," says Fairfax County police Detective Thomas Lyons. "Usually the parent has a job or has ties of some sort. In this case, he just totally broke all ties. She is very concerned.I wish we could do more for her, but I don't know what else would be available."

Patricia Hoff, director of the American Bar Association's Child Custody Project, says child abduction remains a serious problem, involving an estimated 25,000 to 100,000 youngsters a year. There has been, she says, "a slow and subtle . . . consciousness-raising on the part of law enforcement officials at every level." The 1980 law is still being implemented, but with what she called disappointing response from the Justice Department. Social Security's parent locater service, which has been used to locate fathers who have not paid child support, is now available to states seeking abducting parents, but since federal rules for using the service have just gone into effect no states have had time to act. The rules also allow federal authorities in the state, such as the FBI and U.S. attorneys, to request locater service assistance in returning to the states parents who have been charged with abduction.

Although the new law directs the FBI and the Justice Department to assist states in solving state felony abduction cases, Justice continues to limit its role to cases in which there is independent evidence that the child's life is threatened or evidence of severe mental or physical problems or potential injury. But a parent who has no idea where her child is has little chance of establishing independent evidence that the child is in danger.

The Justice Department says there has been a history of prosecutors dismissing cases once the child is found, and says the department only wants to be involved where local prosecutors will prosecute. Justice is also requiring, in the name of fairness and uniform standards, approval from Washington for federal fugitive warrants to be issued so the FBI can enter the case and apprehend the abducting parent.. This, Hoff testified at a congressional oversight hearing, is inefficient and duplicative of the local prosecutor's judgment.

Hoff, citing examples of prosecutors who testified that they do prosecute these cases, says Justice is "painting with a very broad brush," in complaining that these cases are often dismissed. "Increasingly," she says, "at the state level when prosecutors understand they can now get federal assistance to apprehend abducting parents, they're more inclined to go ahead with prosecution." Further, she says, state prosecutors are only going to ask for federal help in the most serious cases.

Parental abduction is a felony in 39 states. It devastates the parent left behind, generally the mother. It traumatizes the children, and has at times endangered them. Congress recognized that federal assistance to the states could help reduce its occurrence, by helping recover the children and deterring potential abductors. An administration that promotes itself as "pro-family," pro-law and order and pro-states' rights has taken a curiously inconsistent position in enforcing the laws against parental abduction.