The National Park Service, confronted with opposition from motorists and local transportation officials, has abandoned its plan to cut off car traffic through a central section of Rock Creek Park, federal officials said yesterday.

Instead, the park service has embarked on a more limited proposal they said was aimed at benefiting bicyclists, joggers and other park visitors. Officials said the agency plans to build a new 2 1/2-mile bike trail in the park. In addition, it would close several sections of park roadways on weekends, starting Aug. 20.

Manus (Jack) Fish, the service's regional director, said the revised plan would provide for "balanced use" of the 93-year-old park and would "better meet both the recreational needs as well as those of the motorist." The modified proposal has drawn "overwhelming support" from the public, he said.

A park service official said the federal agency had dropped its earlier plan, which would have interrupted car traffic on weekdays as well as weekends, after being bombarded with objections from the District of Columbia and Montgomery County governments, the American Automobile Association and many other groups.

Local government agencies warned, the official said, that a curtailment of traffic on Beach Drive--the north-south road through Rock Creek Park used by 10,000 cars on weekdays--would force thousands of cars onto other already congested thoroughfares, such as 16th Street, which is now impeded by construction work.

In addition, the official said, motorists charged that barring use of Beach Drive by commuters amounted to an "exclusionary action." The earlier proposal, however, had gained broad support among bicycling, recreational and environmental groups. "We tried to find a middle ground," the official said.

Under the now-abandoned proposal, which was announced Feb. 16, the park service would have blocked use of a central section of Beach Drive to commuters and other through traffic by closing off the road at Boulder Bridge, starting in 1985. Before then, the park service had proposed to restrict rush-hour traffic to a single lane, leaving the other lane open to bicyclists and joggers.

Under the less controversial plan now being put into effect, the park service will close parts of Beach Drive to cars on Saturdays, Sundays and holidays that fall on Mondays. Similar closings have been tried experimentally by the park service in recent years.

The sections of Beach Drive that will be closed to cars on weekends include 2 1/2 miles between Joyce and Broad Branch roads, a mile between Wise Road and Picnic Grove 10 north of Sherrill Drive, and a mile between West Beach Drive and the Maryland line.

The weekend closings will extend this year from Aug. 20 to Oct. 23. In the future, they will run from the first Saturday in April to the third Sunday in October. The roads will be closed to cars from 7 a.m. on Saturdays to 7 p.m. on Sundays or Monday holidays.

The park service also will seek to extend its 11-mile bike trail network in the park by building a new 2 1/2-mile path along a horse trail beside Rock Creek between Joyce and Broad Branch roads. The trail, expected to cost nearly $1 million, is to be completed in 1986, officials said.