Those strange little parks in downtown Washington with the uncut grass, the tiny triangle of land in the Shaw area cluttered with parked cars, the concrete traffic island near Mount Vernon Square and the grassy patch in Northeast sprouting a tall commercial sign all have one thing in common: They are national parks.

In contrast to the carefully groomed lawns and colorful flower beds gracing the tourist areas around the national monuments, a number of the federally owned miniparks sprinkled throughout the city are difficult to identify because of their deteriorated condition and the absence of signs.

The city has more than 300 federal parks, the majority of which are tiny bits of land measuring less than a half acre and some dating to 1790. A random survey by The Washington Post shows that a number of these parks have been neglected for years and some have been paved for parking lots or expropriated to display commercial signs.

The National Park Service, which has jurisdiction over these urban patches, is unable to report on the condition of all of the parks because the agency does not regularly check on them, according to officials. However, the Park Service inspected eight of the parks after receiving inquiries about them from a reporter.

One of those parks, at Fifth and L streets NW, is being used as a parking lot by the D.C. police department's traffic division.

"It appears that D.C. is using that property and we have no record of a permit for that," said Arnold Goldstein, assistant superintendent for the parks in central Washington.

The smallest park, a 251-square-foot preserve at Florida Avenue and T Street NW, is covered with tar and apparently was first paved in the late 1920s, according to Goldstein. The property adjoins more of the same type of pavement, where the United Cab Association repairs cabs.

"Yes, it is our park and someone, some time ago, did pave it over," said Goldstein, who, with park map in hand, inspected the property with another assistant superintendent.

Sandra Alley, spokeswoman for the National Park Service, said this week that the scattered, tiny parks make Washington a unique city in the federal park system.

"Nowhere else in the country do we have so many small parks," she said. "When it comes to all those little triangles, we have to decide to either keep them up or overlook them in deference to other things."

"We mostly look at them if we get a complaint," she said. "Sometimes someone calls us about a tree down on one of our parks and we have to check the map to make sure it is ours."

Because the Park Service does not regularly check on all of these small parks, in at least one case there was some confusion over who actually owned the property.

John Booker, owner of Coast In Liquors at Florida Avenue and N Street NE, said he believed that he had bought the entire triangle of land five years ago when he purchased his store. At the tip of the triangle is a grassy area with a two-story-high sign advertising the store.

"I thought I bought the whole thing," Booker said. "That sign pole has been there for more than 30 years and no one ever complained to us about it. How am I supposed to know that was park land?"

Booker's night manager, who did not want his name used, said he has been cutting the grass around the sign pole as part of his job at the liquor store.

"I'm going to charge them for all my work if they [the Park Service] ever come out here," he said.

William F. Ruback, the superintendent of the miniparks, said his employes regularly maintain the parks with grass and pick up trash in the ones with trash cans.

David Rolland, who has rented a house at the corner of Florida Avenue and N Street NE for the past two years, disagrees. The point of land just outside his house is national park land.

"Well, I've never seen anyone come here from the government to mow the grass or pick up the trash," he said. "We take care of that ourselves."

Alley said that there are not enough park employes to take care of all of the vest-pocket parks.

Alley said her agency has a program to encourage people to take responsibility for small parks and also for businesses to donate money to the Park Service to use on specific parks.

"We've had great success with the Franklin Park where the business community helps us do a major cleanup every year," she said. "And businessmen around Thomas Circle have donated money to help keep that park planted with shrubs and grass."

"We'd love to have people in the neighborhoods with the tiny parks adopt a park," she said. "You never know, that front yard of yours may be a national park.