Two construction workers suffocated yesterday when the sides of a 30-foot-deep ditch in which they were laying sewer pipe for a housing development in Annandale collapsed, burying them under several feet of earth, Fairfax County police reported.

The accident occurred at 10:37 a.m., witnessed by a foreman and two other workers, who immediately began digging and were soon joined by dozens of rescue workers.

The body of Michael DeGroot, 25, was recovered at 1:25 p.m. Fire officials said he had been buried under five to seven feet of earth.

At 21:15 p.m., the body of Robert Joseph Baker, 25, was dug out from beneath 15 feet of earth, according to County Fire Department Capt. Glen Gaines.

Bruce Jennings, manager of the S.O. Jennings Construction Co. a subcontractor laying the sewer pipe for a 20-home development off Gallows Road and Ashton Street opposite the Woodburn Elementary School, said he was told the collapse "happened within a split second . . . so suddenly no one could do anything."

Gaines said that eight pieces of fire equipment went to the scene, but as his men began digging "we started getting additional cave-in from the loose dirt." He said ladders were used in an attempt to shore up the dirt.

Workers from the William A. Hazel Construction Co. were called to the scene to help shore up the dirt with heavy metal jacks placed across the ditch, according to Bruce Aylor, a company employe.

Rescue workers were forced to dig in shifts because of the 90 degree heat and used hand shovels in addition to a mechanical back hoe, Gaines said.

A county fire department spokesman said there appeared to be no shoring to reinforce the sides of the 100-foot-long ditch. State and federal inspectors who were on the scene for five hours yesterday said they are still investigating the cause of the accident.

Jennings said inspectors told him "there was no wrongdoing on our part. We were within all of the safety precautions as far as we know it."

Gilbert Esparza, area director of the D.C. office of the federal Occupational Safety and Health Administration, said shoring would not be needed where there is compact soil for solid rock. Esparza, who was not on the scene yesterday, said he was awaiting a report from his inspectors.

DeGroot, who lived at 6931 Weston Rd., Fall Church, was the brother of two Fairfax County police officers. He and Baker, 25, of 1832 Stanley Pl., Falls Church, had worked for the Jennings Co. for about two days, Jennings said, but had worked for another company for three or four years.