You may spot him while you're jaywalking -- or maybe you don't see him at all. He uses radar guns, unmarked cars and buses equipped to test for drunk driving.

He is a D.C. Traffic cop, and last year his city had the lowest number of traffic fatalities for any city its size in the country -- 46 -- of which only 16 were pedestrian fatalities.

"It may not seem like much -- until one of your loved ones becomes involved; then it gets very personal," said Capt. Wayne Layfield, Commander of the D.C. Police traffic enforcement branch. "We arrested 3,300 persons who were drunk while driving last year. But what has to be remembered is that we catch only one out of every 2,000."

The record low in traffic fatalities continues a three-year trend in Washington that coincides with quadrupled traffic enforcement and highway engineering safety efforts, according to city officials.

Among the safety features is the famed "New Jersey Wall," a concrete highway divider constructed not only to prevent cars from swerving into oncoming traffic, but to "hug" the car until the driver can regain control.

These barriers have been erected in Northeast and Southeast Washington along the Kenilworth Avenue section of I-295, once a common accident site.There have been no traffic deaths there in two years, since the walls were built.

While traffic fatalities have declined in the city, they are on the rise in Washington's suburbs.

In Montgomery County, police reported 74 traffic deaths through October 1980, one-third higher than the number of fatalities in all of 1979.

In Prince George's County, 98 traffic deaths were reported through November, compared to 103 in all of 1979.

Virginia State Police reported 1,040 traffic deaths statewide through November, compared to 1,011 for all of 1979. Neither the state nor suburban authorities could furnish complete figures for the Virginia suburbs.

I think what's happened is that 1979 was the year of the gas crunch and people didn't drive much," said Virginia State Police Sgt. S. H. Schoaf. p"This year they're adjusting to high gas prices, they're buying smaller cars that get better mileage and that's putting 'em back on the road."

With the passage of right-turn-on-red legislation in the District after years of political battling, city officials may beef up pedestrian traffic enforcement even further. But not without misgivings.

"Jaywalking is the hardest ticket in the world to give out," said Capt. Layfield. "Just about everybody is guilty, but to be singled out is an embarrassment. A lot of people are resentful."

Nevertheless, about 25,000 jaywalking tickets were issued last year, about the same as in 1979. Before the police jaywalking teams hit the streets -- concentrating mainly on downtown during the noon hour -- pedestrian fatalities average about 30 a year.

Layfield said streamlined procedures now permit police to process drivers suspected of intoxication in 30 minutes compared with two hours before. Suspects are required to take a "breathalator" test on equipment carried in a large police van, to determine the amount of alcohol consumption.

Layfield brushed aside a suggestion that increased ridership on the region's expanding Metro subway system may have contributed to the reduction in traffic deaths. He said traffic fatalities in the District began falling before the subway system began significant operations.

"As far as we know, there has been no effect," he said. "The main highways into and out of Washington during the rush hours are still jammed."