In an effort to prove to motorists than the high incidence of traffic injuries and deaths at the intersection of Rtes. 28 and 50 in Chantilly is due to "human error" rather than malfunctioning traffic lights. Fairfax County police are cracking down on speeders near there and trucks carrying overweight loads.

"We wanted to prove to the community and the motorists that they're violating the law," said Capt. Robert L. Ellis of the Chantilly police substation, who held a press conference yesterday to discuss the results of the weeklong crackdown that began last Friday.

Ellis said he ordered stepped-up enforcement efforts, including the use of six additional officers in unmarked cars in the area near the intersection, after a four-mounth survey revealed that although the number of accidents at the intersection had declined by 50 per cent over last year, the number of deaths had increased from two to five.

So far, according to Ellis, police have issued 170 tickets, about half of them to speeders who police said were going at least 10 miles over the 45-mile-an-hour speed limit, and about half to truck drivers, some of whom were carrying as much as 10 1/2 tons in overweight loads.

In the wake of several recent fatal accidents some motorists have complained that the traffic lights at the major four-way intersection south of Dulles International Airport sporadically malfunction, sometimes switching from green to red without a warning yellow, at other times suddenly turning green in all directions.

Ellis emphatically ruled out defective equipment as the cause of the accidents. "Not one accident has been related to defective equipment. They're all alcohol-related or due to human error (like speeding). The state highway department has monitored that light in all sorts of weather and run all sorts of tests and they've found no mechanical failure whatsoever."

Ellis added that motorists with citizens band radios have helped in the crackdown. "One report of a (police) car on the road will slow traffic down within a 50-mile radius because they're not real sure where the police car is. One truck driver from Atlanta told us he had heard before he left there that "there are wall-to-wall mounties in Fairfax County."

Ellis also indentified two victims of a fatal accident that occurred Tuesday a few miles west of the intersection on Rte. 28 as Jon Alex Dimitrijevich, 54 of 1810 Metzeroff Rd., Adelphi, and his wife, Virginia 61. Police said Dimitrijevich drove across the center lane and collided head-on with a truck driven by Jose Manuel Brum Correia, 36, of 1311 Kittredge Ct., Woodbrdge. The accident is still under investigation, police said.