Lt. Col. Joseph E. Vasco Jr., the former acting police chief of Prince George's County, remained in critical condition yesterday at the shock-trauma unit of University Hospital in Baltimore.

Vasco, 44, was seriously injured early yesterday when his police cruiser slid out of control and crashed into a tree on a rural road near Upper Marlboro.

According to police, the accident occurred as Vasco was returning from a visit with the family of Antonio M. Kelsey, a young county police officer who was killed Saturday while chasing a suspect.

A police account said that Vasco was returning home about 12:30 a.m. on St. Thomas Church Road, a narrow, winding street leading to his home. As Vasco was rounding a curve, his car went out of control on an icy patch of the road.

Vasco's car slid down a 20-foot embankment and struck a tree head on.

He was pinned behind the steering wheel of his car for about one hour.

Vasco radioed for help to a police dispatcher. He was taken to Prince George's General Hospital in Cheverly by a state police helicopter, and was later flown to the shock-trauma unit in Baltimore shortly after 3 a.m.

Police said Vasco had suffered from a fractured at the base of his skull, a collapsed lung, and a severed bronchial tube. He also suffered broken ribs and a leg injury.

Hospital officials said Vasco was undergoing a five-hour operation late yesterday.