An Alexandria judge forwarded a murder charge against a 27-year-old city worker to a grand jury yesterday after a detective testified the man told him he angrily struck a forceful blow to his girlfriend's 2-year-old son shortly before the child died.

Homicide investigator Derrill Scott said that Mark Anthony Hines, a sanitation worker, became enraged after he discovered that the child had taken food from a refrigerator without permission.

Scott said Hines hit the child's head with the back of his hand on the morning of Jan. 23. The blow was so forceful that it knocked the child onto a metal toy truck, causing further injuries.

"When I asked him to show how hard he hit the child," said Scott, "he reared back with his left hand and hit me hard and I stumbled forward."

Alexandria Juvenile and Domestic Relations Judge Joseph L. Peters Jr., who sent the case to the Circuit Court grand jury, also heard a medical expert testify that the child died of injuries that could not have been sustained in a fall.

"You would need severe pressure to cause those internal injuries," said Dr. Gregory Wanger, assistant chief medical examiner in Northern Virginia. "They were consistent with blows."

Annette Ligon, the mother of the dead boy, was living with the defendant at 726 S. Fayette St. when her son, Curtis, died.

She said yesterday that the child appeared well when she left him with Hines.

She said that Hines called her at work about 11 a.m. and asked her to return home immediately. When she arrived, Curtis was on her bed, unconscious, and Hines had telephoned for help.

An emergency squad arrived within minutes, but efforts to revive the child failed, one of the unit's members testified.

Ligon said that she had lived with the defendant for five months and that she believed he took good care of her son.

James C. Clark, Hines' lawyer, had attempted to close yesterday's hearing to the public.

It was opened at the request of lawyers representing The Washington Post.

Hines is free on $50,000 bond.