No attacks have been reported in two unrelated series of sexual assaults in Prince George's County since police began publicizing the episodes, but detectives said the two suspects have continued to elude them.

Police officials said they are looking into each new clue as they search for the man they think raped eight boys in Hyattsville during a 3 1/2-year period and another man believed to have raped nine young women over two years near the New Carrollton Metro station.

Sgt. Dave Carter, head of the county police sex squad, said last week that there have not been any recent attacks.

The last assault in the New Carrollton area, according to police, was in late February when two young women walking behind a store in the 7400 block of Annapolis Road were raped. The last Hyattsville case involved a boy attacked in the woods behind Northwestern High School in January, police said.

"I suspected they would go underground" after the attacks were publicized a few weeks ago, Carter said.

He explained that investigators are in a dilemma when deciding whether to warn the public about such serial crimes at the risk of tipping off suspects, who then often alter their pattern of behavior or temporarily disappear.

Since police first began publicizing both series of crimes early this year in their "Crime Solvers" efforts, Carter said, his unit received about a dozen calls, but most were useless, often because callers could give only scanty information. "What we need are details, like license tag numbers" or full names, he said.

Carter said he has had undercover officers on surveillance at Northwestern High School and the New Carrollton Metro station in the past, and that he plans to do it again, but he pointed out that his staff is limited.

In 1984, eight investigators worked on 413 sexual assault cases, he said. In addition, he said, "Some of the older victims don't want to be bothered with questions from police . That's part of their life they don't want to remember."

The mother of one of the boys attacked most recently in Hyattsville said "police have been very silent" about the case in recent weeks.

She said she has heard of no new attacks but is concerned that "the kids are using the park again," referring to the wooded area near the high school where many of the assaults have occurred.