Turning 13th Street Northwest from a four-land commuter road during rush hour back into a two-way street has not cut down on the number of cars commuting through the area, a University of Maryland study concludes. It merely forces motorists onto nearby streets.

The study, funded by the Highway Users Federation which opposed the change, also reports that travel time and the numbers of traffic delays have increased slightly for commuters using the four-mile stretch of 13th Street between Logan Circle and Georgia Avenue.

"The changeover has failed to reduce traffic congestion, save energy or produced cleaner air" as District offficials claimed it would, Federation director W.W. Rankin said recently during a meeting of the National Capital Area Transportation Federation. The transportation group, composed of representatives of many bus, taxicab and trucking companies, local businesses and the American Automobile Association, opposes the 13th Street change and other impediments to motor vehicle travel around the Washington area.

D.C. Department of Transportation Director Douglas Schneider, disputes the basic conclusion of the study -- released last week -- although Ranklin announced some of its conclusions at the federation meeting.

Schneider says the city's own traffic surveys show that since the change went into effect Jan. 7, traffic in the 13th Street corridor has dropped by 250 to 500 cars during the morning rush hour. The corridor includes 13th, 14th and 16th streets and Georgia Avenue.

He also questions the validity of the study's pre-Jan. 7 traffic survey. It counted rush-hour traffic on Dec. 18 and 19, the week before Christmas when many area residents already had left on holiday. District traffic counts, made last fall, found 16,750 to 17,000 cars traveled the 13th Street corridor between 7 and 9 a.m. on weekday mornings. Recent city counts show an average of 16,500 cars now using the corridor.

But Schneider insisted the main benefit of the change has been the 50 percent reduction in traffic along 13th Street itself, a residential street where a number of houses are less than 30 feet from the roadway.

The average speed of traffic on 13th Street also has declined to about 20 miles an hour, Schneider said. Before the change traffic averaged about 30 miles an hour, with cars frequently clocked at speeds up to 50 and even 60 miles an hour on what in effect was a four-lane highway, Schneider told the group. The speed limit on 13th Street is 25 miles an hour.

Rankin said the study shows delays have doubled on 13th Street from two to about four an hour, and travel time on the four-mile section has increased 3 to 5 minutes or 18 percent. Rankin also said the delays and longer driving time have increased gasoline consumption and air pollution, and made the 13th Street corridor more dangerous.

As to the delays caused suburbanites commuting by car, Schneider said the travel time has been increased "by only four minutes on that street. I don't think that's too much to bear . . . nor does the mayor or the city council. That's the way we feel in this community. And I don't feel that it is punitive . . . I'm not against cars, although we're not going to accomodate everyone who wants to drive into Washington, one person to a car. We simply don't have the resources to handle that."

Schneider and the District have been criticized by the two federations, the AAA and some suburban officials for allegedly making automobile commuting more difficult in order to support Metro and to reduce air pollution and traffic congestion in the nation's capital.