A construction supervisor died in a deep earthen tomb yesterday when a muddy retaining wall collapsed over a drainage pipe ditch alongside a country road near Seat Pleasant.

W. Thomas Sparr, 40, owner and chief supervisor of Sparr Construction Co. of Baltimore County, was replacing 36-inch storm drainage pipes under Fernwood Road when the wall caved in on top of him and two of his workers.

While the two workers were able to pull themselves out of the ditch, Sparr was buried so deeply that it took Prince George's County firemen nearly an hour to recover his body, fire and police officials said.

Cause of the cave-in has not been determined. James Kramer, a steam-shovel operator who was picking up sandwiches for the Sparr workers when the accident occurred, said it appeared that the steel jacks which were holding up the retaining wall "just gave out."

Sparr's 19-year-old son, Eric, was one of two workers injured in the accident. He suffered a leg injury and was reported in good condition last night at Prince George's General Hospital. The other trapped worker, Warren Heydt of Kingsville in Baltimore County, was treated and released.

"We got here a few minutes after the cave-in was reported, around 12:45 p.m.," said Fire Capt. Duncan Munro. "One man (Heydt) had pulled himself out, but another (Eric Sparr) was trapped to his waist. When he was being dug out there was another partial collapse. We never saw the third victim until it was too late."

Sparr was replacing the drainage pipes as a subcontractor for the Washington Suburban Sanitary Commission. WSSC officials said contractors who work for them are responsible for safety conditions at the job site.

County rescue workers said it appeared Sparr died of suffocation. The official cause of death has not been determined by the state medical examiner's office in Baltimore.