BOSTON (AP) _ Even though they are ''terrific parents,'' Patricia and Cleveland Riddick must give up the 3-year-old boy they raised from infancy because the child's natural aunt now wants him, the state confirmed Thursday.

''This is a real heartbreaker. No one is pretending this is easy,'' said Janet Eustis, assistant commissioner of the state Department of Social Services, which oversees adoptions.

''No one is faulting the Riddicks. They were terrific parents. But the department has decided that in the long term, it will be in the child's best interest to be with relatives,'' she added. ''The position of the department is to place a child with relatives whenever possible.''

''Getting Michael was a miracle to us,'' said Mrs. Riddick, 41. ''I've had him since he was six days old. They are going to take him away over my dead body. Believe me, they (the courts) are going to know me.''

The state expects to hand Michael over to his aunt in California, whom it will not identify, after a Probate Court hearing on July 31, Ms. Eustis said.

''The state of California has investigated the (aunt's) family,'' she added. ''We believe they are an excellent home.''

In January 1984, the couple took custody of an unnamed newborn at Boston City Hospital who had been given up by his mother and rejected by every relative contacted by the DSS.

Ms. Eustis said the Riddicks were legally named the child's pre-adoptive parents. ''We had planned all along that adoption would be the plan for this child,'' she added, noting that adoption proceedings often take more than three years to complete in Massachusetts.

The Riddicks named the boy Michael, and settled with him in a new home in Dorchester. Riddick continued to work as a maintenance man for a realty firm, while his wife quit her job at a dry cleaner's to care for the child.

Several months ago, Michael's aunt - his mother's sister - contacted the state and said she had changed her mind about taking custody of the boy, Ms. Eustis said.

''The circumstances have changed'' in the child's natural family, she said. ''In the long run, provided there can be a smooth transition, this will be for the best.''

But the Riddicks say Michael does not want to leave them.

''Don't feel sorry for me,'' Mrs. Riddick said. ''Feel sorry for my kid. Right now, he's a very happy-go-lucky kid. We're his mummy and daddy. He doesn't like strangers. We're all he's known all his life.''