To the whooping applause of about 50 outdoors devotees, the National Park Service yesterday closed a two-mile stretch of Beach Drive in central Rock Creek Park to weekend motor-vehicle traffic.

Bicyclists and joggers gathered at noon with Park Service officials for ribbon-cutting ceremonies at the intersection of Broad Branch Road and Beach Drive -- the southern end of the section now closed to all Sunday, Saturday and holiday traffic. The section has been closed to autos on Sundays for several years.

The scenic stretch, which park officials said is little used by weekend motorists, hugs Rock Creek and twists north from Broad Branch Road past deep woods and small waterfalls to Joyce Road just south of Military Road.

"How terrific!" exclaimed Terry Myers, 35, a bicycling enthusiast. Myers has not biked much in that area because -- unlike other sections of the park -- this section has no bike path. Bicyclists have had to compete on Saturdays and holidays with cars zipping along the narrow road. "I will use it regularly from now on," Myers said.

The section has been closed to motor vehicles on Sundays since 1972. The Park Service had experimented with closing the section on Saturdays as well, but decided several years ago to reopen the road to motorists because bicyclists and joggers were not using it enough.

"The bicycle store up there at the northernmost point of the two-mile section ran out of business then," said Rock Creek Park Supt. James Redmond. "Now bicycling as well as jogging has really picked up tremendously."

Redmond said the Park Service will monitor recreational use of the road until next June to determine whether the weekend closing -- which runs from 7 a.m. Saturdays to 7 p.m. Sundays and the same hours on holidays -- should be made permanent. "We'll see how the public responds," he said. "If they are using it, we'll keep it closed to motorists . If not, we'll open it back up."

Bob Bers, executive director of the Washington Area Bicyclists Association, said extension of the closing to Saturdays will be "a tremendous help to promoting bike commuting. People from Maryland are looking for a route to come down into the city ."

Bers and other biking enthusiasts said they would also welcome a weekend closing of Beach Drive north of Joyce Road. The Park Service and the Washington Metropolitan Council of Governments are studying the possible impact of additional closings in the area.

Peter Harnik and Michael Replogle, the principal organizers of the People's Alliance for Rock Creek Park, a group of 18 environmentally minded organizations supporting the Saturday closure, said the alliance's next move is to encourage more bicyclists and joggers to use the road. "We will now get the word out. People can now use the most beautiful part of the park," Replogle said.