Skateboarders attracted to the multilevel arrangement of open-air parks in downtown Washington have cracked, scraped and defaced some of the monuments, causing one National Park Service official to call for stronger enforcement of regulations prohibiting skateboards in the parks.

A granite block cracked three months ago by skateboarders had to be replaced at Pershing Park on Pennsylvania Avenue, at the base of a memorial wall outlining the battles of World War I. Officials discovered a crack last week in a second granite block nearby.

"They ride up the memorial wall," said Trumelle Satterwhite, who works at the Pershing Park concession stand. "I am sure they are destroying the letters of the memorial."

But the urban skateboarders -- many in their mid-teens and more interested in stunt-boarding than flat speed skating -- say they are being unfairly pushed out of public spaces, and that they should be allowed to practice their sport on at least part of the stone and concrete expanses in the capital.

"Memorials are like a waste of money," said 15-year-old Shaun Persinger of Warrenton, Va. "These people are dead; they don't have any relatives; there is no use" for the wasted space.

The Pershing Park memorial, dedicated to the 2 million Americans who served overseas during World War I, cost $5 million six years ago.

National Park Service officials have no estimates as to the amount of damage that is being caused by the skateboarders, but Vinston Corbin, a Park Service building engineer, said he had asked officials to investigate ways to enforce regulations barring skateboarders from parks.

Corbin said the skateboarders had also caused some damage to nearby Western Plaza, particularly on the steps and concrete blocks where many office workers sit during their lunch hour.

Corbin said he is concerned about the safety of pedestrians in the plaza because skateboards scraping along the concrete blocks have whetted the edges.

Persinger acknowledged that some skateboarders practice jumps on skateboards, landing on the granite, or glide along the edge of a step with the steel frame of the skateboard. But "we don't cut every rock in the park," Persinger said.

Skateboarders are not the worst defacers of national monuments these days. Park Service officials say sightseers prospect for souvenirs at the Jefferson and Lincoln memorials, ink religious graffiti on the Washington Monument and leave thousands of mementos.

But skateboards may be the most common -- and with their grating wheels, the most annoying -- instrument of damage at the parks patronized by residents.

Corbin said skateboarders have been cruising in the midtown parks for at least three years, but only recently has damage to the parks been serious. At Pershing Park, careering skateboards have left white scratches on the walls and chipped a number of the steps. Park officials are planning to consult a stonemason on the damage to the parks.

Park Service officials said regulations bar skateboards in national parks except in areas specifically designated for them.

Corbin said he had called U.S. Park Police once every three weeks to report skateboarders at Western Plaza or Pershing Park, where he says a whole van of skateboarders sometimes unloads. But Corbin said many of the skateboarders stay only half an hour and are gone when police arrive.

Ruquayya Freeman, a crew leader at the Pershing Park concession stand, said she calls police four or five times a weekend when skateboarders come to the park.

"They need to make a park where they can skateboard so they won't come over here," Freeman said.

According to some skateboarders, Pershing Park was once the most popular city park for skateboarding because of its accessibility by subway and its central location.

But Brian Tucci, 15, of Northwest Washington, said Park Police had forced many skateboarders to find other places to practice.

"It makes me feel bad that someone who did this {to the monument} will make it harder for skateboarders," Tucci said. "People have run us out all over the city."