WASHINGTON -- Washington's Pennsylvania Avenue, sometimes called "America's Main Street," is being 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 told The Associated Press on 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, including M. Paul Friedberg and Carol Johnson. 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.

The Washington-based foundation, created in 1998, aims to educate people about historic landscapes through training programs, partnering with local groups and publicity for at-risk spaces. It has a track record of saving threatened landscapes by raising awareness with its annual Landslide listing.

Eleven other sites are being added to the group's Landslide 2012 list, which will be announced Thursday at an event with New York's Central Park Conservancy. They include Los Angeles' Hannah Carter Japanese Garden, Nasher Sculpture Garden in Dallas and New York's Jones Beach, a public beach and park designed by Robert Moses in the 1920s that continues to draw 6 million to 8 million visitors each year.

This year's list also honors the patrons who helped create such notable spaces. For Washington, it was the federal Pennsylvania Avenue Development Corp., which funded improvements but disbanded in the 1990s.

"Back in the old days, great buildings, great landscapes, great art collections were the result of great patronage," Birnbaum said. But this year's listings are "dying a quiet death because of deferred maintenance and neglect."

The historic corridor may see new development, though, as Donald Trump recently won rights to redevelop Washington's Old Post Office into a luxury hotel. Birnbaum said such big investors on the avenue could add pressure to change the design.

In some ways, designed landscapes are more complicated to preserve than a single historic building. Putting off maintenance can quickly accelerate their decline, Birnbaum said.

In Los Angeles, the Japanese garden has become the focus of a legal dispute. It was given to the University of California Los Angeles in 1964 by former regent Edward W. Carter. But the school listed the property for sale this year without notifying Carter's heirs.

The popular Jones Beach on New York's Long Island is a state park that once was a model for others nationwide. Now it's suffering from strained budgets. Embellishments designed by its original architect have slowly been lost. Brick walkways were replaced with asphalt. A mahogany railing along the boardwalk was replaced with aluminum. Water fountains and plants have been removed because there's little staff to tend such gardens in a struggling economy.

"Now it functions as a park, but it's lost that extra level that made it premiere," said Alexandra Wolfe, preservation services director for the Society for the Preservation of Long Island Antiquities, who nominated the beach for the listing. "We wanted to call out the fact that this is also a designed landscape."

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