D.C. homicide detectives were unsure yesterday whether it was by accident or design that a Silver Spring couple drowned in the Potomac River late Monday afternoon.

"This is a very bizarre case," said homicide detective Norman Brooks.It may take us a week of investigating."

The couple, Eric L. May Jr., 35, and his wife, Annie Margaret May, 36, of 15105 Centergate Rd., drowned after the car in which they were sitting plunged down a boating ramp into the water at Gravelly Point north of National Airport.

Homicide detectives appeared to be leaning yesterday toward the belief that an accident had led to the drowning. "This was a semi-professional couple, making it," Brooks said. "Why would they have wanted to die?

"It could have been a stuck accelerator faulty brakes."

Brooks said detectives would examine the car within a few days, as soon as it dries out. The couple did not leave a suicide note.

One witness told police the couple had been sitting in the parked car for some time and appeared to have been arguing. But one detective yesterday questioned whether there had been an argument.

"A lot of people talk with their hands," he said. You don't know whether they were arguing unless you actually heard them."

Police said they had not determined who was driving or why the couple had driven to Gravelly Point.

Eric May was a safety inspector for the Nuclear Regulatory Commission; his wife was a researcher at the cancer institute of the National Institutes of Health. The two met and were married in the 1960s, while they were students at St. Augustine's College in North Carolina. About five years ago, they moved into a large two-story, red brick house in the Stonegate subdivision of Silver Spring. They had two children, Eric, 5, and Korry, 2.

Yesterday, neighbors in the subdivision said they were convinced the deaths were accidental.

"They were the most stable couple," said one neighbor, Irma Sprangle. The fact that they're trying to say it wasn't an accident is completely out of the ball game.

'They were a close-knit family and there was a lot of love there."

Neighbors described Eric May as an outgoing, friendly man who frequently invited them to eat with his family at cookouts, to watch football games with him on television, and to use his basketball court. His wife was described as a quiet woman who spent most of her free time inside, cooking or caring for her children.

"Even if you saw Eric two or three times in a day, he'd always give you a big hello," said one neighbor, Bettie Lou Nash."He was the first person to come over and welcome us when we moved in."