Prince George's County police are trying to solve two series of sexual assaults -- one against eight boys that started more than 3 1/2 years ago and the other against at least nine girls and women that started last April.

Neither of the apparently unrelated series of attacks has been widely known in the northern Prince George's communities where they occurred, although both have been made the subject of the county's "Crime Solvers" program in recent days in which $1,000 rewards are offered on televised announcements.

One citizens association was kept advised informally by police officers who patrol the area and police began circulating composite drawings of suspects in recent weeks.

Yesterday, reporters calling homes and businesses in the areas of the attacks had difficulty finding anyone who knew they had occurred. Some citizens expressed alarm at the situation and the fact that they had not been informed.

Police officers questioned yesterday acknowledged that they frequently find themselves in a quandary over when to release information about rapes.

One county sex squad detective said that if incidents are publicized too soon a rapist may go "underground," discontinuing at least for a while activity that investigators might focus on in apprehending him, or may move to a new location. The detective also said police fear that the information may incite "copy cat" crimes.

Police spokesman Bruce Gentile said his department began to publicize the attacks in recent days because investigators had run out of new leads.

The series of assaults on boys began in July 1982, and the most recent one occurred early this year, police said. The boys, aged 12 to 15, were attacked by a man wielding a broken bottle in a large field behind Northwestern High School and behind a bowling alley near the Prince George's Plaza shopping center. The man often attacks two children at a time, threatening to hurt one if the other runs away, police said.

The rapes of girls and women aged 11 to 27, the most recent of which occurred last month, were in the West Lanham Hills area from Annapolis Road (Rte. 450) east to Whitfield Chapel Road. The victims were usually jogging or walking to or from the nearby New Carrollton Metro stop early in the evening or early morning and were accosted at knifepoint.

Judy Tagart, 38, supervisor of a shop in the 7900 block of Annapolis Road, near the site of some of the attacks on women, learned yesterday of the assaults. "I'd like to know things like this are going on so maybe I could prepare for it . . . be a little more observant," she told a reporter. "When you don't hear about things like this you get lax."

Employes of several other businesses in the same block said they had not heard about the rapes.

James Dean, president of the West Lanham Hills Civic Association, said police officers have informed his organization of the rapes over the last two years. He said the information is passed along at association meetings but he worries that the news is not widely spread because the meetings are not well attended.

Peter Blauvelt, head of security for Prince George's schools, said one of his investigators assisted police by questioning some Northwestern High School students about the series of assaults against boys some time ago. There has been no formal warning of students, he said.