WASHINGTON — Washington’s Pennsylvania Avenue, sometimes called “America’s Main Street,” is listed among the nation’s endangered landscapes because of neglect and deferred maintenance by the National Park Service.

The grand avenue connecting the Capitol and White House is slowly falling into disrepair, the nonprofit Cultural Landscape Foundation said Wednesday. Water fountains rarely function, benches are broken and some trees have been removed.

In the 1960s, President John F. Kennedy called for a revitalization of Pennsylvania Avenue. Improvements included the creation of small parks designed by top landscape architects. But they haven’t been maintained.

“There really is this kind of very slow downward spiral that is happening,” said Charles Birnbaum, the group’s founding president.

Except for part of the road that was redesigned as a pedestrian plaza in 2004 for security in front of the White House, “the lion’s share of the 1.2-mile stretch hasn’t been renewed,” Birnbaum said.

National Mall Superintendent Robert Vogel said in an emailed statement that the park service is working on ways to preserve and restore Pennsylvania Avenue, though he did not elaborate.

“We welcome the interest and support of the Cultural Landscape Foundation and the attention they can bring to this effort,” he said.