A bulldozer operator who was a co-worker of two men killed in an Annandale construction site cave-in two years ago testified yesterday the construction methods that allegedly led to the accident were unsafe but are common practice in Northern Virginia.

Richard Payne Jr. testified in U.S. District Court in Alexandria he had been concerned that the trench in which Robert Baker and DeGroot were laying sewer pipe was not wide enough and improperly sloped. But he said that in four years of working with heavy machinery in Northern Virginia he had become used to working under similar conditions.

Baker and DeGroot, both 25, were buried and killed when the trench collapsed on July 18, 1978.

The trial that began yesterday is the first prosecution in a federal crackdown on allegedly unsafe construction working conditions in Northern Virginia.

The defendants are the S. O. Jennings Construction Corp. and its two top officers, S.O. Jennings and his son, Burce Jennings. They are charged with three counts of violating federal safety regulations for allegedly failing to keep excavated materials away from the edge of a 19-foot-deep trench and brace the sides of the trench.

State officials have said they found at least a dozen previous trenching violations by the Jennings company in the last 12 years.

Payne testified yesterday he believed that the construction right-of-way in which the sewer line was being lain was too narrow to be safe.

The trench that eventually collapsed became steadily deeper as work progressed, he said, but there was no room to make it wider and, in the absence of protective bracing, to make less steep its slope to the bottom where Baker and DeGroot were working.

"We needed at least 20 feet more on either side of the ditch," Payne said. "About the entire cut, we needed more room. There was never any question of that."

Payne said he had approached his superiors prior to the accident about widening the construction area so that 10-foot mounds of dirt could be moved away from the edge of the trench. He said the idea was vetoed in favor of saving a line of nearby trees.

"They said we couldn't cut down any more trees," Payne said. "The neighbors would complain about the noise" if the trees were gone.

The cave-in occurred around 10:30 a.m. as Payne was fetching a load of gravel to spread over the pipe. Baker and Degroot were at the bottom of the trench, maneuvering the pipe sections and directing the bulldozer operators above.

When the 135-foot-long ditch collapsed, and initial slide buried Baker and DeGroot up to their waists, co-workers later recalled. second avalanche buried both men.

Bruce Jennings and S.o. Jennings could be sentenced to up to six months in prison and $10,000 fines on each of the three counts against them if they are found guilty. The company faces more that $24,000 in additional OSHA fines, which are pending disposition of the case.