GRANITE CITY, Ill. (AP) _ A 7-year-old with AIDS-related complex encountered dozens of angry parents Thursday as he joined other first-graders in class Thursday after months of isolation in a nearby trailer.

''He looked like he was ready to cry,'' Jason Robertson's mother, Tammie, said after she walked her son to Prather Elementary School.

''They threatened me and my son on the way in and on the way out,'' she said of the protesters. ''They said playing with Jason was like playing with a loaded gun.''

Jason had been the lone student in a trailer on the school grounds since Nov. 16 and had been tutored at home previously. On Wednesday, U.S. District Judge James L. Foreman ordered him back in the classroom in response to a suit by the American Civil Liberties Union.

Thirty students stayed away from the 750-pupil school because of Jason, and five more left during the day, said Gilbert Walmsley, superintendent of the Granite City schools. In Jason's class, 28 of 30 pupils attended.

Mrs. Robertson said Jason ''said that his day went well and that he made a lot of friends. The teachers said that they (classmates) were all fighting over who would get to play with him.''

The boy, a hemophiliac, apparently became infected with the AIDS virus through a contaminated blood product, officials said.

After school, Mrs. Robertson said roughly 40 angry parents met her and Jason outside, chanting, ''Back to the trailer.'' She said about 30 children then surrounded her and her son, telling the crowd, ''Leave him alone.''

''The children were wonderful,'' she said.

The symptoms of AIDS-related complex include swollen lymph glands, low- grade fever, drenching night sweats, weight loss, extreme fatigue and chronic diarrhea.

Twenty percent of patients with ARC will develop AIDS within two years, scientists say. Researchers do not yet know if the rest of them will go on to get AIDS after a longer period.