Beginning this weekend, an additional 1.5-mile section of Beach Drive in upper Rock Creek Park will be closed to motor vehicle traffic on weekends and holidays for the rest of the summer, the National Park Service announced yesterday.

A two-mile section above the zoo, which has been closed to weekend traffic since last August "has brought an overwhelmingly favorable response" from bicyclists, joggers and users of the 92-year-old federal park, according to Park Service spokeswoman Sandra Alley.

The Park Service will experiment with the expanded weekend closings until Oct. 3, when it is expected to propose permanent traffic restrictions in the park. A public meeting is scheduled for Oct. 15 to discuss the permanent restrictions, with a final decision expected to be made in November by regional Park Service director Manus (Jack) Fish.

The weekend closings, urged by a coalition of about 20 area outdoor and environmental groups, are among 10 traffic options being studied for Rock Creek Park by the Park Service. The options, designed to reduce heavy commuter automobile traffic in the park, include a possible permanent ban on cars in the park's narrow upper section.

A study by the Metropolitan Washington Council of Governments this spring concluded that restricting or even banning traffic on Beach Drive would have little impact on local traffic.

A top New York City transportation official and Thomas Downs, director of the District Department of Transportation, last summer urged the Park Service to increase traffic restrictions in Rock Creek Park, as has been done in New York's Central Park, which is now closed to auto traffic except in rush hour.

The section of Beach Drive closed on weekends since last summer extends from Broad Branch Road about a mile north of the zoo to Joyce Road. The additional sections to be closed extend from picnic groves at Sherrill Drive to Wise Road and from West Beach Drive to the Maryland line. Traffic will be banned from 7 a.m. to 7 p.m.

Except for a 100-yard section, permitting cross-park traffic from Wise Road to West Beach Drive, these are the only portions of Beach Drive where bicyclists and pedestrians must use the roadway. A separate bicycle trail exists in most other sections of the park.