Tears flowing down her face, Mary Thompson swept her 5-year-old son, Anthony, off his feet and gave him a big hug. "You're going home," she said as his round face lit up with a smile.

Anthony stood in the Northwest home of his foster mother and looked back at his mother. "I always thought I was going home for Christmas," he purred.

Such was the reunion yesterday between Mary Thompson and her son, who was taken from his mother four weeks ago by D.C. authorities who claimed the child had unexplained traces of barbiturates in his blood and mysterious marks on his arms that might have been needle tracks. Officials accused his mother of neglect and a D. C. Superior Court judge ordered the child placed in a foster home.

But yesterday, Judge George H. Goodrich agreed that Anthony could go home to his mother for an extended Christmas visit after an attorney representing the youth told Goodrich that the child would be in no danger if he were returned to his mother. "The child is homesick," the attorney said. "There is a very strong bond between the mother and child."

The attorney also said that from her investigation, she has not been able to determine that the barbiturages were given to Anthony by his mother. "I don't feel we will ever know how that happened," the attorney said.

A social worker and an assistant Corporation Counsel, speaking for the city government, also agreed that Anthony should be allowed to go home.

In releasing Anthony to his mother's care until a Jan. 6 court hearing, Goodrich warned that is anything happened to the child, the mother would be held responsible. "My sole concern is the welfare of the child," he said.

"Thank you, your honor," Thompson said, beaming from ear to ear.

She rushed out of the courtroom to a pay phone where she called her mother to tell her the good news. "'T' is coming home," she shouted over the phone.

Dorothy Sharp, Thompson's mother, said later she had prayed that the judge would return her grandson to her daughter. The happy grandmother said she planned to take the family out to dinner to McDonald's, her grandson's favorite eating spot.

"I feel like I just gave birth to a baby," Thompson said. "All these weeks [since the court took custody of her son], I feel like I've been in labor. Now I feel like I just gave birth."

As Thompson waited in the court corridor for arrangements to be made for her to pick up her son, various social workers who knew of her case came by to congratulate her.

"I'm so glad you got him back," said one.

"I don't even know how I feel," Thompson said. "I have mixed feelings. I'm glad to have him home. But I still think they went about it in the wrong way."

Anthony was taken away from her on Nov. 20 after a series of events that began when her son told a teacher at Parkview Elementary School that a doctor had stuck needles in his arm and showed the teacher the marks.

School officials, fearing the marks may have come from drug injections, called city social workers, who in turn contacted police.

The police took the child to D.C. General Hospital for an examination and ordered blood tests. Traces of two barbiturates -- amobarbital and secobarbital -- were found in the child's blood. Both drugs are used in several children's medicines, but not in Triminic, a cough syrup that the mother said was the only drug she had knowledge of her child taking.

She said the needle marks and the story the boy told the teacher probably came from the blood and tuberculin skin tests the boy had taken three weeks earlier.

Shortly after the blook samples were taken four weeks ago, Dr.joseph Schutt-Aine, the pediatrician in charge of the case at D.C. General Hospital, said the marks on the boy's arm could have been needle injection sites but could also have been caused by a minor injury. "They would not strongly suggest needle marks to me," he said.