A proposal by the National Park Service to close Beach Drive NW in Rock Creek Park for several hours on weekdays has drawn opposition from community activists worried about spillover traffic in their neighborhoods.

Mayor Anthony A. Williams, who once endorsed the idea, is now having second thoughts about closing a major traffic artery out of town while the city is on heightened alert for possible terrorist attacks, he said last week.

The draft proposal, published in the Federal Register on March 14, would close three segments of Beach Drive in the northern portion of the park to cars and other vehicles on weekdays, from 9:30 a.m. to 3:30 p.m. The proposed closure would affect Beach Drive between Broad Branch Road and Joyce Road NW, the section that is closed to motor vehicles on weekends.

"I'm amazed that in a city that has the worst traffic in the United States, that they would even consider closing a major thoroughfare at any time," Tim Letzkus, president of the 16th Street Heights Civic Association, said yesterday.

The association won't take a formal vote on the proposal until its next meeting April 8. But Letzkus said he doubts that residents in the 14th and 16th Street corridors and other affected communities will feel positive about an action that could clog their streets with motorists heading north and south.

Williams (D) once supported closing sections of Beach Drive to motor traffic as an experiment, but he doesn't think the time is right for more traffic restrictions. "In the context of the heightened threat level and transportation problems we're having right now in the city, it's really premature" to close Beach Drive, the mayor said on WTOP's "Ask the Mayor" radio program.

Mayoral spokesman Tony Bullock said Williams liked the idea of preserving more of the park for bicyclists and pedestrians -- but that was before the Sept. 11, 2001, attacks.

The Washington Area Bicycle Association and the People's Alliance for Rock Creek, which have long pressed for more recreational outlets in the park, support closing Beach Drive to cars and other traffic.

The plan was one of three proposals for Beach Drive that were published in the Federal Register, although the Park Service has called the closure option its "preferred alternative." A second proposal would implement high-occupancy vehicle restrictions on Beach Drive during rush hours, and a third would permanently close certain segments of Beach Drive north of Broad Branch Road to traffic to promote non-motorized recreation in that area of the park.

Bill Line, a Park Service spokesman, said yesterday that closing Beach Drive during non-rush hours "would improve the use of the park's resources and enhance educational opportunities, including increasing interpretive activities with park rangers."

He stressed that all options, including making no change, will be discussed at public hearings in early May. No dates have been set, he said, but the Park Service is working to arrange a convenient location for two evening hearings.

An environmental impact statement analyzing the three proposals can be viewed at www.nps.gov/rocr. Written comments are due by July 15 and can be e-mailed to rocr_superintendent@nps.gov or sent to Superintendent, Rock Creek Park, 3545 Williamsburg Lane, NW, Washington, D.C. 20008.

Staff researcher Bobbye Pratte contributed to this report.