The street-wise, nearly naked prostitute stands limply in the middle of the cheery green and white McDonald's, eating a hamburger and sipping a root beer. She looks over the crowd with vacant, uninterested eyes. She isn't working. She's on a break.

Lines of other customers bob and weave in endless, slightly seasick motion. The place is alive with the aroma of fried food and filled with odorous whiffs of perfume, smoke and liquor.

It is 3 a.m. and business at McDonald's at 14th and K streets NW is booming.

On the street, in the glow of the golden arches, a prostitute coos, "we do it all for you," pirating the hamburger chain's advertising slogan as she peddles her own menu of fast pleasure along the city block that is Washington's magnet for night vice.

At this corner, the hub of streetwalking business in Washington, McDonald's seems far from the all-American image, it has carefully created through a collection of bouncy jingles, thousands of kiddie birthday parties and a gaggle of characters with names like Mayor McCheese, Hamburglar and Ronald McDonald.

Here, McDonald's takes on the burlesque hue of the late-night traffic, attracting virtually every imaginable customer.

Mingling with the prostitutes who are decked out in peacock colors men flow in and out of McDonald's from the clubs and movie houses along 14th Street from H Street NW to Thomas Circle.

At the food lines, and at the small, plastic tables, there is a different kind of regular crowd here, too-the office works with nowhere else to go in the middle of the night. And there are the beat patrolmen, conspicuous in uniform, and the vice squad detectives sure-footed and clear-eyed despite the hour.

To keep the loitering at night to a minimum, McDonald's officials have posted signs limiting customers to 20 minutes to eat. The public restrooms are closed at night.

"We limited the time and beefed up the management," a McDonald's official said.

The official said most of the 14th and K Street business is done during the routine noon lunch hour, but with the heavy, late-night traffic, it makes good business sense to stay open.

"We've worked with the Board of Trade on this-the prostitues congregate outside," the McDonald's spokesman said. "They were here before we were."

McDonald's stays open until 2 or 3 a.m. on week nights, and stays open all night on Fridays and Saturdays, the busiest nights of the week for the restaurant and the streetwalkers.

Detective Tom Grave, a veteran of the vice squad who is assigned to a prostitution control office, said, "personally, it's a good thing" McDonald's is open. "They offer decent food and they don't offer anything bad for the community."

Grace said the McDonald's security guards try to keep the crowds moving, but there are "incidents."

For example, he said, a prostitute passed out on McDonald's floor.

In the last few years, the main street prostitution business has drifted down from Logan Circle and Thomas Circle, where urban revitalization is under way, to the blocks bordered by 14th and 15th Streets and K and L Streets.

The McDonald's corner at 14th and K, is broad and well lighted, a perfect promenade for the women. With the warm spring weather, their business has picked up considerably, police said.

Prostitution flourishes along 14th Street because it is accessible, Detective Grace said, "You can be on 14th Street, get your business done, and be back . . . in Virginia in a few minutes," he said.

The traffic has been so bad that beat patrolmen have blocked off the K Street service road in front of McDonald's. "It was a different kind of service road at night," one said.

While prostitution openly clutters these few city blocks, police worry about spin-off crimes: muggings, robbery and nightclub ripoffs of drunk customers.

Grace said increased competition among the women means that the less successful ones have to steal or rob to make their "quotas" for their pimpes.

Arrests for prostitution are difficult. "Just because a woman's dressed in hot pants and has her blouse opened to here," Grace said, pointing to his ravel, "is not legal reason to arrest her."

A patrol car cruises by a woman who has been standing at the curb in front of McDonald's waving to passing cars. She stops waving for an instant while the squad car eases by. In the glow of its taillights, the woman climbs into a car that follows behind.