The novelist would probably call it Light Case of the Mysterious Traffic Lights." Like a good mystery, it has lots of people baffled.

Some motorists claim that a four-way bank of traffic lights, located at the intersection of Rtes. 50 and 28 in Fairfax County, behave capriciously, at times switching suddenly from red to green without a warning yellow, at other times turning green in all directions.

They say that the sporadic malfunctions have been responsible for two serious collisions, including one fatal mishap last week, several less serious accidents and an untold number of near collisions.

Police and state highway officials say that whenever they investigate, the lights are working fine.

In the accident last week, police said Queenie May Carlton, 69, of Martinsburg, W. Va., was killed when a car driven by her daughter, Ida, 22, made a left-turn through the intersection on a red light after waiting through three changes of lights in the other direction to get a green light. The Carlton car was struck by a second car.

Police said that because the Carlton vehicle didn't pass over a magnetic detecter in the roadway, the left green turn signal was not triggered.

The Carlton car was struck broadside by a car driven by Merle Rivas, 32, of Sterling Park.

Police say Rivas was driving westbound on Rte. 50 through a green. Neither Carlton nor Rivas could be reached for comment. Police said they are still investigating the accident.

Harry Moser of Fairfax City said he had another kind of problem with the lights at the intersection. Several weeks ago, while traveling east on Rte. 50 he drove through a green light. When he reached the middle of the intersection he noticed traffic approaching on his right. "My light suddenly jumped from green to red," he recalled.

In order to avoid oncoming traffic, Moser said, he swerved into the median strip, causing the trailer he was hauling to jacknife.

"I told police the light jumped and they didn't even question me," he said. "They seemed to know all about it, but the light was working then. When I told my insurance company they said they'd had a similar claim a few weeks before at the same intersection. And when I got back to the office and told the story other people told me about accidents there."

Wayne Dawson of Burke was one of the people who told Moser about a serious accident which occurred in 1975. Dawson said that his father was one of two drivers involved in a collision that demolished both cars.

Both drivers at first claimed the other had run a red light. However, Dawson said, "When the police came they looked at the lights and found they were green in all four directions. They directed traffic until someone came to fix the lights."

Neither driver was charged, Dawson said.

Scott Trais of Clifton said he drives through the intersection every weekend on his way home from college. He said he has seen a four-way green light "at least two or three times in the past year." Travis noted, "Sometimes you'r cruising through there at 45 (m.p.h.) and people are coming at you the other way."

Donald Keith, resident engineer with the Virginia Department of Highways and Transportation said that the lights are equipped with a fail-safe mechanism designed to trigger a flashing red when there are two green lights in opposite directions.

Keith said his crews have inspected the light several times in recent weeks, as the result of motorists complaints and the accident that killed Mrs. Carlton. Each time, he said, the lights have worked properly.

State traffic supervisor Julian Brown said, "If we can find anything wrong, we'll replace it, but we spent hours there (monitoring the lights) and we cannot catch it malfunctioning."