If you want to see where the war on litter is being won, visit Saunders Park in West Philadelphia.

It once was so dirty, overgrown, and misused that it was called "Crack Park." Today all that litters its green expanse are pink petals from cherry blossoms.

If you want to see where the war is being lost, cruise by Old York Road and Lindley Avenue in North Philadelphia. The rusted underside of a railroad trestle shades a dumping ground for bricks, beer bottles, boxes, and construction debris. Sometimes the odd piece of furniture turns up.

"We're not even sure where it comes from," said Sylvia Okechukwu, business-district manager of the Logan Community Development Corp. Clean it up and "the trash magically reappears."

On Saturday, thousands of volunteers will join in the fifth annual Philly Spring Cleanup, the centerpiece of the Nutter administration's commitment to a cleaner city. They will seek a different kind of magic: helping the city try to shed its clinging, distressing image as "Filthadelphia." In the last two years, volunteers have carted off 2,580,580 pounds of trash and litter with the assistance of everything from shovels to brooms to front-loaders.

"The movement is growing - and this is a movement," said Deputy Streets Commissioner Carlton Williams. "There's hope for the city. We're definitely changing the attitudes of people, but we still have a long way to go."

The city "litter index," which grades areas on a six-point scale, shows that many parts of Philadelphia have gotten dirtier. The number of "extremely" or "excessively" littered areas has grown from seven to 47 in four years.

It's important to view the cleanup not as a one-day event, Williams said, but as the kickoff to a year-round effort that includes other public-service projects such as UnLitter Us.

Yet it's a movement that has failed to achieve permanent change, despite the onerous impact of litter on everything from property values to quality of life. Community leaders talk about the difficulty of trying to change litterbug habits, but they cannot explain why litter abides even as public-health campaigns to reduce smoking and drunken driving have been wildly successful.

"Have I seen a difference? The answer is a big Y-E-S. But it's a work in progress," said Tracey Gordon, a Windsor Street block captain in Southwest Philadelphia.

Across America, cities, counties, states, businesses, and property owners spend an estimated $11.5 billion a year to pick up litter - more money than the total economic output of the Bahamas, five times the gross domestic product of Greenland.

And that's only the direct cost. The indirect cost may be greater, and more concentrated on homeowners and consumers. Estimates are that litter blight, by itself, decreases property values 7 percent.

In neighborhoods, studies show, litter is as much a sign of deterioration as graffiti, vacant lots, and abandoned houses. A recent Baltimore survey found that on blocks that had more litter, people had higher estimates of drug sales, harassment and street fights.

What's more, experts say, litter begets litter - and the opposite is true, too. People who enter a clean area tend to avoid littering. But if the place is dirty, they become more likely to litter.

For instance, in the Kensington area, especially along Frankford Avenue, success varies from street to street. On blocks where even one resident has stepped forward to lead cleanup efforts, the improvement shows. On blocks without leaders, places already defined by empty buildings and drug dealers, trash is as constant as the night.

In Kensington, two part-time workers clean four commercial corridors at least once a week. The problem is that the streets are dirty when the workers arrive, clean when they leave, and dirty again when they return.

"The blocks where people care," said Carla Castillo, a leader at New Kensington Community Development Corp., "those blocks tend to be cleaner."

Saunders Park covers most of a city block at 39th and Powelton, set against the back of its owner, Penn Presbyterian Medical Center.

What did it take to transform the park? Everything.

Money. Time. Energy. People. Commitment.

"But it's what we do," said James Wright of the People's Emergency Center, which helped lead the effort.

The Pennsylvania Horticultural Society had approached Presbyterian, joined by the Bank of America and Saunders Park Neighbors Association. They cut the ribbon on a revitalized green in 2009.

"This little park does mean a lot to the community, more than most people would realize," said Gary Ginsberg, assistant executive director of facilities at Presbyterian. "It helps enhance all the good things that the community is and should be."

Workers eat lunch there. Neighbors walk their dogs. Drexel University students kick soccer balls, and on some evenings older people play bocce.

The park has stayed clean - Presbyterian pays to cut the grass and to have a maintenance person sweep up.

But litter is insidious. The sidewalks on the half-block walk from the park to Lancaster Avenue are awash in trash: A toilet seat. Two pillows. A discarded wooden box that once held clementines.

"It's gotten better," said Kira Strong, director of community development at PEC, "but a lot of people still comment on, 'Wow, there's a lot of trash.' "

Last year Travel and Leisure magazine named Philadelphia the second-dirtiest city in the nation, behind only New Orleans, a town that had nearly been wiped out by a hurricane.

"We want to encourage people: Take pride in your community, take pride in your neighborhood," said the Streets Department's Williams. "People have to change their mind-set to not throw trash on the street."

About 300 cleanup projects will commence Saturday, led by Mayor Nutter.

"I think he has done more on this issue than any of his predecessors, and applaud these efforts," said Mary Tracy, director of Scenic Philadelphia, formerly called SCRUB. But until people change, "we are a long way from having clean streets in Philadelphia."

Cigarette butts are the most common type of litter in America, accounting for 57 percent of the waste. Food remnants and wrappers account for 34 percent.

America's roads are marred by an astounding 51.2 billion pieces of litter, according to a study by Keep America Beautiful. That computes to 6,729 pieces of litter per mile, everything from bits of paper to abandoned cars.

Those numbers are actually an improvement.

The total, piece-by-piece estimate of road litter has dropped 61 percent since 1969. Similarly, the number of people who admit to pollsters that they have littered in the last month has dropped from 50 percent in 1968 to 15 percent in 2008.

Why does litter persist?

One reason is that, well, we keep picking up the litter.

Northeastern University economist Harlan Platt studies unintended consequences - how the effort to accomplish one goal often leads to other outcomes. He says at least some litter is actually the unexpected result of cleanup programs.

" 'I don't have to be fastidious, because this organization will clean up for me,' " said Platt, author of Unintended Consequences: How to Improve Our Government, Our Businesses, and Our Lives.

The amount of litter in Philadelphia can shock visitors and newcomers.

"It's astonishing," said Angie Williamson, director of economic development at the New Kensington Corp., who came here from southwest Virginia. "I know it's in a lot of cities, but it seems like Philadelphia has this culture of 'Littering is OK.' . . . It's a long and slow process to get folks to change a lifetime habit."

at 215-854-2415, jgammage@phillynews.com, or on Twitter @JeffGammage.