Controversial traffic restrictions tested on Reno Road since last August have done exactly what city officials and residents hoped they would do.

They have reduced and slowed traffic along the winding residential street that for several decades has been a major commuter route for suburban Maryland drivers.

A recently completed city traffic study found:

* Morning rush-hour traffic has dropped 27 percent along the 34th Street-Reno Road-41st Street corridor since last summer.

* Average rush-hour traffic speeds have dropped from 22 miles an hour to 15 miles an hour.

* The number of traffic accidents and traffic noise levels have dropped, as more than 850 cars have shifted to Connecticut and Wisconsin avenues during morning rush hours.

* Traffic on half a dozen residential side streets crossing Reno Road has increased, however, as motorists apparently seek alternate routes.

Although the traffic restrictions have pleased many Reno Road residents, the overflow problem has brought protests from people living on the side streets.

The District Department of Transportation will hold a public hearing tonight to hear public comment on the Reno Road restrictions before deciding whether to make them permanent. The hearing will be held at 7:30 p.m. in the Woodrow Wilson High School auditorium, Nebraska Avenue and Chesapeake Street NW.

The city report not only indicates that transportation officials may make the restrictions permanent, but also states that the city, after consulting with local residents, "will impose additional traffic control measures" to handle traffic problems on side streets.

The city also indicated in its report that it may restrict northbound Reno Road traffic to one lane, thus permanently limiting the road to one lane in each direction. This would impose the same restrictions on evening commuter traffic that have been imposed on morning traffic for the past seven months.

From 1968 until last fall, one of the three lanes along the Reno Road corridor has been reversible during rush hours, permitting two lanes inbound in the morning and two outbound in the afternoon.

The reversible-lane policy enticed commuter traffic onto the hilly, winding road, and furthered the city's post-World War II transportation policy of making Reno Road an "arterial highway," along with Wisconsin and Connecticut Avenues. In 1946, the city cut down trees and widened Reno to three lanes, linking it to 34th and 41st streets to make an alternate north-south auto route.

The Reno Road Traffic Coalition, which lobbied successfully in recent years for traffic restrictions, including 15 mph speed limits near two elementary schools, is now supporting restrictions on evening rush-hour traffic and on side streets, according to coalition chairman Herbert Reff.

"We feel anything that restricts rush-hour traffic in residential areas is a positive contribution. . . . We want one lane in either direction" along Reno Road, Reff said.

"In Bethesda and Chevy Chase, they've gone to extremes to protect their residential neighborhoods by completely prohibiting parking except for cars with residential stickers," said Reff. "We're not trying to ban traffic, only reduce it in our residential areas."

Reff said his group has a petition signed by more than 700 residents urging that the southbound Reno Road restrictions be made permanent and extended to northbound traffic, and that the city work to reduce traffic problems on side streets.

However, some residents don't believe it's possible to stem the tide of suburban Maryland commuters, who constitute 70 percent of rush-hour traffic along Reno Road. They believe the only way to get the commuters off side streets may be to return Reno Road to a major commuter route--a position supported vigorously by the National Capital Area Transportation Federation, a 20-year-old group that lobbies for car, truck and bus groups.

Federation Executive Director Harold Gray said last week that restrictions on Reno Road "are an inconvenience to a great majority and a minor inconvenience to only a few hundred residents along Reno Road."

Jane Gilbert, of 3433 Porter St. NW, a member of a Porter for People Committee, said her group opposes traffic restrictions on Reno Road because they have "transferred problems from one area to another to another . . . to the side streets." The group has circulated a petition signed by more than 200 residents requesting stop signs at two intersections, speed bumps and "No Left Turn" signs to deter shortcuts down Porter.

"The traffic has really changed the character of our street," said Gilbert. "It always was a through street, but now it's a highway, with backups, speeding and volumes of traffic we've never had before . . . and a child was struck by a car and seriously injured April 1st, at 37th and Porter."

It is not clear from the city traffic study whether the increased traffic on side streets is due to the restrictions on Reno Road, since traffic may have been affected by other factors, including the expansion of McLean Gardens and the recent opening of Metro stations at Van Ness, Cleveland Park and the National Zoo.

On side streets such as Albemarle, Brandywine, Fessenden, McKinley, Yuma and Porter, the biggest increases in morning traffic actually have been for west and northbound traffic--heading in an opposite direction from downtown rush-hour traffic.

While morning rush-hour traffic decreased by 870 cars along Reno Road, it increased by 820 cars on Connecticut and by 330 cars on Wisconsin--overall morning rush-hour traffic having increased in the Northwest area by 280 cars compared to last summer.

Despite the higher volume of traffic on Connecticut, traffic speeds on the avenue increased marginally (from 19.9 to 20.3 mph). On Wisconsin, with only a slightly increased volume of traffic, rush-hour speeds decreased from 19.7 to 16.6 mph.

Malfunctioning traffic signals on Wisconsin have been a major reason for slowed traffic there, said the report. Traffic signals on Connecticut have been improved, helping speed traffic along that avenue.

Accidents along Reno, Connecticut and Wisconsin have decreased by 9 percent, and the number of injuries by 40 percent, in the five-month period after Sept. 1, the report states. Reno Road accidents dropped from six to one. Overall this means the traffic changes "created a safer environment on Reno Road without increasing accidents on the two other major routes," the study concludes.