An Alexandria man charged with murder in the death of his girlfriend's 2-year-old son pleaded guilty yesterday to involuntary manslaughter, acknowledging in Alexandria Circuit Court that he struck the child in anger after the boy littered their kitchen.

Mark A. Hines, 25, a city sanitation worker, was arrested after Curtis Ligon, 2, was found dead in the apartment that the boy's mother and Hines shared.

On Jan. 23 the child pulled many items out of the refrigerator, littering the kitchen floor, and Hines, angry because Curtis was supposed to be sleeping, struck the boy, according to a statement of facts Hines signed.

The blow caused Ligon to fall stomach-first on a metal toy truck, prosecutors said yesterday.

Worried that the child was seriously hurt, Hines said, he called his girfriend at work and asked her to return to their 726 S. Fayette St. apartment.

Ligon said she found her son lying pale and unconscious on her bed. One hour later he was pronounced dead at Alexandria Hospital.

Dr. Gregory Wanger, an assistant Northern Virginia medical examiner, ruled that the child died of abdominal injuries "consistent with blows." Wanger said the child's lethal internal injuries could have been caused only by "severe pressure," and not simply a fall.

Hines, a short, stocky man who recently served in the military, told prosecutors he had planned to marry the child's mother, Annette Ligon.

Circuit Court Judge Albert B. Swerksy postponed Hines' sentencing until Aug. 13, to allow a psychiatrist to evaluate Hines' mental condition at the time of the incident. Hines faces a maximum of 10 years in prison and a $1,000 fine.