WASHINGTON (AP) _ Guerrilla attacks on the nation's curbs and handrails may be set for a big slide forward.

Security guards who have to protect the curbs and railings may be set for a big headache.

Up to now, the activity called grinding generally has been reserved for adventurous skateboarders and in-line skaters. They leap onto a curb or railing, trap it sideways between their wheels, and slide down.

However, because of a technological step forward, grinders no longer need boards or skates. Companies make shoes with special grinding surfaces in the arches. With the shoes, a grinder can walk to a site unobtrusively and attack without warning.

Pioneering grind shoe manufacturer Soap Shoes of Torrance, Calif., has a grooved plastic plate. And Rollerblade, which earlier pioneered the in-line skate, has expanded its line to include a grind shoe with a pair of metal rollers.

Either way, the result is a tongue-in-groove effect designed for sliding.

``It's an exhilarating feeling,'' said grinder Matt Jacobsen, 22, of Concord, Calif., who tested shoes for Rollerblade. ``It's kind of like ice. It's a smooth feeling.''

Unlike skates, the shoes can be worn anywhere, allowing spur-of-the-moment grinds, Jacobsen said. ``You jump up and you land,'' he said. ``People stop. Their jaws drop and they are completely confused about what's going on. It's a lot of fun.''

What's more, guards who are looking out for in-line skaters won't see a member of the shoe crew coming, Jacobsen said. So the guards can't try to head off the shoe-clad grinders as they do skaters, he said. ``In the skates, they cause a little more problems,'' he said. ``They hassle you.''

Authorities who have to keep grinders from wearing down curbs and railings _ as well as colliding with pedestrians _ don't consider their safety patrols to be hassling.

``The defacement of a new public building is always a big concern. Even more than that, I worry about the the safety of the passersby,'' said Rachel MacLachlan, security director for San Francisco's public libraries. Many of the libraries have cement outcroppings that appeal to grinders.

As it is, trying to clear out the grinders is ``like waving at flies,'' MacLachlan said. ``It's very difficult to physically effect an arrest.''

As a company that guards an image of responsibility, Rollerblade doesn't want to appear uncaring about risks to pedestrians or damage to buildings by people wearing its grind shoes.

``We've designed them to be ideal on curbs,'' said Rollerblade's president, Dennis Shafer, in Eden Prairie, Minn. It takes a really skilled rider ``to slide down a 30-foot length of steps without killing yourself,'' he said. ``The other 90 percent will jump on a curb and see how far they can go.''

And Soap Shoes prides itself on using plastic grind plates, said Chuck Morris, the company's president.''I won't put metal in grind plates; I think that's irresponsible,'' he said. ``We did not want to harm people's planters or handrails or whatnot out there. It seems the worst we do is leave a little plastic residue.''

Salespeople say the shoes are moving fast. ``We sold hundreds,'' said the president of New World Sports of San Francisco, Jim Hutchinson Jr. And the companies' presidents see a lot of growth ahead.

``I'd say we have less than 1 percent penetration,'' Morris said.

``The target market is a bored 10-to-15-year-old male, and there's a lot of them,'' Shafer said. ``If it captures all the 10-to-15-year-olds, that's a huge market.''

Most of the interest is in urban areas, experts say. ``New York is doing well for us,'' Morris said. And a lot of the interest is in Europe, he said: ``We are on fire in Holland,'' he said.