KAISER, Mo. » At state parks across the nation, this is the toll of the deepening budget crisis and years of financial neglect: crumbling roads, faltering roofs, deteriorating restrooms.

Electrical and sewer systems are beginning to give out, too, as are scores of park buildings, some of them built by the Civilian Conservation Corps during the Great Depression. In a few places, aging bridges have been detoured and tunnels blocked off because of falling debris.

The tough economy has made money scarcer for administrators at some of the country’s most treasured public spaces who have been forced to postpone maintenance and construction projects, creating a huge backlog of unfinished work that would cost billions of dollars to complete.

Park managers say they try to funnel money to the most urgent needs. Others have received help from private groups or volunteers to tackle work they cannot afford on their own.

"We do what we can," said Denny Bopp, a supervisor for the Missouri district that includes the Lake of the Ozarks State Park, more than 150 miles southwest of St. Louis. The park’s centerpiece is a huge man-made reservoir that attracted more than a million fishermen, campers, boaters and vacationers in 2010.

Many states had backlogs long before the economy started to decline. But the lack of revenue has allowed more sites to decay, and no one can say how long the work will have to wait. At the Lake of the Ozarks, the list of needed repairs includes a historic home with a severely sagging roof and holes in the porch, and a restroom facility covered in moss.

The Associated Press sought information from park administrators across the nation and consulted researchers and published reports. An analysis of data showed that the backlog of projects has ballooned to more than $7 billion and continues to grow.

Park officials say federal stimulus efforts have offered little help for the 6,500-plus state parks, recreation areas and historic sites. And they contend a federal conservation fund to support recreation areas has skewed toward federal facilities.

Site managers and park advocates worry that putting off maintenance work risks making repair projects more expensive, just as a house in need of new shingles will eventually require an entire roof if the first signs of trouble are ignored.

Robin Dropkin, executive director of the advocacy group Parks & Trails New York, said recreation areas can only be allowed to decay so far before visitors stop coming or facilities must be closed for health and safety reasons.

"Who wants to go into a restroom that is falling apart?" Dropkin said.

More than a dozen states estimate that their backlogs are at least $100 million. Massachusetts’ and New York’s are at least $1 billion. Hawaii officials called park conditions "deplorable" in a December report asking for $50 million per year for five years to tackle a $240 million backlog that covers parks, trails and harbors.

In Missouri the list of repairs surpasses $200 million. Michigan initially reported a backlog of more than $300 million, although that might improve a little. Renovations could get under way in 2011 at an historic beach house at Ludington State Park, which has been waiting at least five years to begin the work.

"Everyone seems to have sort of similar issues: Nobody has a lot of money, and everyone has a lot of projects to do," said Will Harris, director of the Maine Bureau of Parks and Lands.

The National Trust for Historic Preservation declared state parks and historic sites to be among the nation’s most endangered historic places earlier this year. The group cited construction backlogs, closures and other budget cuts.

Another risk is that if parks attract fewer visitors, they also bring in less money for the state and for nearby communities. The National Association of State Parks Directors estimates that the parks generate $20 billion in economic activity annually.

Ken Caplinger, director of West Virginia’s parks, said park supervisors are doing their best to avoid cutting activities and services most important to visitors.

"With ingenuity and a lot of elbow grease and hard, above-and-beyond-the-call-of-duty work, you can disguise for a long time a significant lack of funding," he said, "but eventually you have to pay the piper. Eventually it does catch up to you."

Some visitors have started to notice.Sean George, a camper and hiker who frequently visits Missouri’s parks, said the bathrooms and other facilities can be used, but they clearly need work. Many of the sites looked like they "could use a little TLC," said George, 38, of Columbia, Mo.