WASHINGTON (AP) _ The disappearance of 5-year-old Melissa Brannen from a Christmas party in Virginia and the kidnapping by a masked gunman of 11-year-old Jacob Wetterling in Minnesota terrorized their communities.

But they are the exception, not the rule, for abducted children, according to a Justice Department study released Thursday.

The overwhelming majority of the 359,000 children kidnapped each year are taken by relatives, the study said.

Nevertheless, 200 to 300 kidnappings a year are dramatic enough to prompt headlines and are what the public generally perceives when it hears about an abduction - a stranger forcibly taking a child for a long period of time and possibly killing the victim.

The Brannen and Wetterling cases last year fit this definition of the stereotypical abduction created by he researchers who compiled the study, ''Missing, Abducted, Runaway, and Thrownaway Children in America.'' Neither child has been found.

As many as 4,600 children are kidnapped by people who are not relatives in abductions that can include rapes and assaults. Many of these kidnappings never attract the public's attention, according to the researchers, David Finkelhor of the University of New Hampshire, Gerald Hotaling of the University of Lowell in Massachusetts, and Andrea Sedlak of Westat Inc.

The fact that only 1.4 percent of all abductions of children are committed by strangers should ease parents' fears of strangers, said Ernie Allen, president of the National Center for Missing and Exploited Children.

''We don't want parents to be paralyzed by fear,'' he said, adding, however, ''If there are 300 Melissa Brannens a year, that's 10 elementary school classrooms full. That's a tremendous concern.''

The study says the estimate of 4,600 abductions ''may be low. A number of these ... abductions may never be reported to the police because the victims of these assaults or rapes are ashamed or intimidated,'' the study said.

The study was required by the 1984 Missing Children Act.

Overall, the researchers estimated that in 1988 there were 354,100 children abducted by relatives, up to 4,600 kidnapped by non-family members, 450,700 who ran away, 127,100 who were thrown away - abandoned or deserted, told to leave the home or told to stay out after leaving voluntarily - and 438,200 who were lost or were otherwise missing.

The study said 114,600 children may have been involved in attempted kidnappings, with the majority involving strangers unsuccessfully trying to lure the children into automobiles.

The study said many children thought to be missing actually were not: ''Caretakers did know where they were. The problem was in recovering them.''

The report also said that at least 22 percent of the children previously considered runaways should be treated as throwaways.