A $45 million traffic computer system was turned on yesterday by District officials, who said drivers should now have an easier time negotiating the city's 1,300 intersections with signal lights.

The most immediate change drivers can expect to see, officials said, is fewer malfunctioning signals, which they said would improve the flow of traffic. But motorists aren't likely to notice a dramatic difference for several months, when the lights will be adjusted more often during rush hours.

Installed in the last five years, the new system is one of the largest of its kind in the nation, city officials said. It replaces the deteriorated traffic signal network built in the late 1950s that often held up thousands of drivers in Washington.

"For those of you who have lived or worked in the District before this year, you may remember traffic delays caused by malfunctioning signals or have complained about synchronization," said John E. Touchstone, D.C. public works director. "Those days are now memories."

Mayor Marion Barry flicked on the system shortly after 3 p.m. yesterday at the city's new traffic signal control center at the Reeves Municipal Center at 14th and U streets NW. Barry said the federally financed system "would make life a little bit easier for all of us."

Months from now, as the 47 employees operating the system become more familiar with it, they will be able to do such things as adjust signals several times during rush hour, according to the volume of traffic at a particular location. Under the old system, it was possible to adjust signals only once during rush hour.

For example, said District traffic chief George W. Schoene, traffic heading south on Connecticut Avenue NW from Chevy Chase Circle to Calvert Street NW from 7 a.m. to 7:30 a.m., generally can pass through most intersections with signals by traveling at 28 mph.

By 8 a.m., as rush hour traffic builds, it is impossible to make it through most of the intersections without stopping. By adjusting the timing of the signals, Schoene said, it may be possible for drivers to travel on most of the street without much interruption.

As the system has been gradually installed, hundreds of lights already have been hooked up and signal malfunctions have steadily dropped over the last three years, especially in the downtown area, officials said. But yesterday, 95 percent of the system was turned on for the first time.

The problem with the old system was that it relied on electromechanical timers with dials, relays and motors. That made the equipment vulnerable to extreme cold and heat.

Between 80 and 100 signals a day broke down, causing snarls and confusion for drivers. There was no two-way communication between signals and city officials; the only way the city learned about trouble was when someone called in.

The new system consists of signals equipped with computer chips linked by about 400 miles of cable to six area computers stationed throughout the city's 69 square miles. When a malfunction occurs, officials said, the area computer notifies the master computer at the traffic control center.

Then, engineers can dispatch repair crews and adjust the timing of the other signals in that area.

Already, Schoene said, officials have noticed a drop in malfunctions, to about 15 a day. As the new system becomes fully operational, that figure could drop further, he said.

Another advantage to the new system is that the parts are electronic, making them less susceptible to weather problems, officials said.

Officials said the new system also should enhance synchronization of signals.

One of the chief complaints about driving in the District is that the street lights often are not synchronized, which means drivers pass through a series of lights freely and then suddenly hit a red light at the next intersection, forcing them to stop.

Under the old system, the city only had three light-timing plans: morning rush hour, evening rush hour and a plan for all other times. The new scheme gives engineers more options, including synchronizing the lights for special events, holidays, emergencies and other reasons.

In other words, city officials will be able to tailor the timing of signals to the number of vehicles using a road at a particular time of the day.

On July 4, for example, Schoene said city engineers will tinker with the signals on Pennsylvania Avenue, the Whitehurst Freeway, Canal Road and Foxhall Road to speed traffic home from the Mall.

Consultants studying the system said it would also reduce gasoline consumption, cut daily travel time and eliminate thousands of tons of automobile pollutants.