A two-mile section of Beach Drive in upper Rock Creek Park will be closed to motor vehicles on all Saturdays, Sundays and holidays beginning Aug. 29, the National Park Service says.

The narrow, scenic section of the 91-year-old park has been closed to motorists on Sundays for more than five years, and the park service "experimented briefly with Saturday closings two years ago, without any problems," park service spokeswoman Sandra Alley said this week.

The two-mile stretch above the National Zoo, between Broad Branch and Joyce roads, is a section of Rock Creek that has no bicycle trail and where bikers and joggers compete with cars.

The weekend closings, ordered by regional park service director Manus (Jack) Fish, will permit increased recreational use of the park and not affect weekday commuter traffic, Alley said. The closings will begin at 7 a.m. on Saturdays and end at 7 p.m. Sundays and holidays.

The park service has been studying possible traffic restrictions in the park for more than a year and may impose more restrictions next spring, after Metropolitan Washington Council of Governments traffic study is completed.

Fish's decision to begin weekend closings on Beach Drive, one of 10 "alternative" traffic options the park service is studying for upper Rock Creek, was spurred by last month's visit of New York City's top transportation planner, Samuel Schwartz, and by support for the idea by the chief D.C. transportation official, Thomas M. Downs.

Schwartz said New York's gradual closing of both Central and Prospect parks to cars, except for weekday rush hours, has had virtually no impact on Manhattan traffic and increased use of the parks "tremendously."

Downs suggested the park service might start with weekend closings, as New York did with Central Park in 1967, followed by weekday closings in "off-peak" hours and then possibly closing one lane of Beach Drive to traffic permanently.