Because Maryland Commuters now can ride Metro Trains to work downtown, the District of Columbia announced yesterday that it will end reversible one-way traffic on 13th Street NW and restore it to two-way traffic starting in January.

The residential street has funneled one-way traffic into Washington in the morning rush hour and back to Montgomery County in the evening since soon after World War II, when a building boom produced thousands of new suburbanites to drive to their jobs.

People who live along the four-mile route have "complained bitterly for years at what they call the 13th Street freeway," Douglas N. Schneider Jr., director of the D.C. Department of Transportation, said in announcing the decision.

The idea has been under consideration since 1976. Schneider said next Jan. 7 was chosen as the effective date because the federal government plans to start charging all its employes for parking in October, Montgomery County plans to expand its Ride-On shuttle bus service in December and Metro plans to increase the frequency of its Red Line trains to Silver Spring in January.

As far as he knows, Schneider said, the decision represents the first instance in this country in which a city has deliberately curtailed an automobile-carrying arterial because a new mass transit line has been built parallel to it.

One reason for building Metro, he said, was to reduce the region's dependence upon auto traffic.

The affected section of 13th Street extends from Logan Circle, at N Street NW, northward to Missouri Avenue. One-way reversible traffic continues to a few blocks further north along Piney Branch to Georgia Avenue.

Traffic moves toward downtown from 7 to 9:30 a.m. and away from downtown from 4 to 6:30 p.m., with signals synchronized to keep traffic moving four lanes abreast at a steady 30 miles per hour. At all other times, traffic is two-way.

James E. Clark, an assistant director of the transportation department, said 13th Street carries 3,000 cars during the busiest morning hour, compared with about 2,700 on parallel 16th Street.

The change in January will provide two lanes in each direction at all times, with relatively heavy traffic and signal synchronization continuing, Clark said.

The announcement was made seven months in advance to provide time for ample advance publicity and to give auto commuters plenty of time to plan new travel patterns.

"We want people to know what we're doing and why," Clark said. "If its' not understood, there will be a lot of complaints and controversy."