Someone is sleeping in Joe and Karen McFadden's Fiat. Every morning they find the ashtray emptied and their food wrappers thrown away. A blanket they used to stuff under the seat is neatly folded.

"Whoever it is keeps it neater than we do," said Karen McFadden, a 25-year-old nurse.

The McFaddens are now used to this guest as well as the one who occasionally sleeps in their doorstoop. They live in San Francisco's Haight-Ashbury. Such things are to be expected.

Two fashionable young women lunch at a Haight restaurant, nibbling demurely at their food. As they rise to leave, a ragged young man in an Army coat lurches over to their table, crams their leftovers into his mouth and runs out. No one bats an eyelash.

A full decade and a half after hippies flocked to Haight-Ashbury in 1967 for their "summer of love," a countercultural milestone, the allure of the neighborhood remains. Despite the influx of young professionals, trendy boutiques and posh eateries along the eight-block stretch of Haight Street, anywhere from 25 to more than 100 street people still haunt the Haight daily like bedraggled apparitions; reeking of filth, alcohol and clad in the hippie clothing of a bygone era.

Most of the hippies are gone. So are the crash pads that once housed them. They've been "gentrified" to high-rent renovated Victorians, leaving the remaining flower children wilted and homeless. By day they congregate in rowdy clusters in front of the Haight cafes and shops whose owners let them linger. Hair long and matted, bedrolls by their sides, some are barefoot and many hold bottles of screw-cap wine swathed in paper bags as they beg from passers-by.

At night they turn nearby Golden Gate Park into a virtual Sherwood Forest; a dark and wooded netherworld of latter-day gypsies and beggars. "You poke a bush, you find a sleeping body," grumbles park director Joe Destresky, often irked when the street people burn benches for warmth and fail to use rest rooms.

Others crawl into any crevice they can find to sleep; doorstoops, cars, store entrances--any place that affords protection from San Francisco's chill night fog and unrelenting wind. But in the morning they are back at their posts on Haight Street, clutching bundled belongings and begging money for a cup of coffee.

"You can survive on Haight Street for nothing," brags Juliet, a 25-year-old musician in a red beret who doesn't want her real name used. Like other younger street people, she was drawn to the neighborhood by its hippie reputation.

"You just have to play the street like a fiddle." She takes showers at the tennis courts at Golden Gate Park, hangs around a cafe until someone leaves half an omelette and sings with her guitar case open for several hours every afternoon. "I've lost my middle-class fear of failure," she says. "It's a tremendous freedom."

Juliet hails two friends, strapping young men with hair streaming down their backs and Grateful Dead emblems on their jackets.

"Hallelujah, I'm a bum," crows one. "I don't have to worry about rules. I don't have to get up and go to work to get something to eat. In a dumpster you can get better food than you can in a restaurant, and half the time it's still warm. There's enough wasted in this country to feed the world," he says.

Juliet and her friends, mostly white and in their 20s and 30s, are out on Haight Street by choice, unlike the thousands of hard-bitten ex-cons, released mental patients and displaced elderly who inhabit the sleazy high-crime downtown slum called the Tenderloin.

"This is not Skid Row," insists Betty Mosias, one of the Haight Street shopkeepers who champions the street people. "That's a whole little society out there with its own ethics and values."

Vestigal peace-and-love hippie ethics persist to some degree. According to the police who walk the Haight beat, the street people don't commit such serious crimes as gambling, prostitution, heroin dealing, mugging, rape or stealing. These are not mean streets.

"Everyone tries to be cool," explains Juliet, "because if someone gets out of line the heat comes down on all of us."

Like Juliet, some of the street people are musicians and poets. But many are alcoholics or drug burnouts who took one hit of acid too many in the '60s. Some collect disability or welfare, but others are too spaced out to contend with the bureaucratic red tape required to receive government assistance.

Instead, the Haight's street people put themselves at the mercy of the street. Often the street comes through. Cast-off mattresses and foam pads find their way to the street people's cubbyholes. Boxes of used clothes appear on street corners. Cafes feed the street people their scraps.

The Haight-Ashbury Free Medical Clinic, a nonprofit, walk-in center staffed with volunteer doctors, tends to their cuts, venereal disease, lice, absesses and scabies.

Not all merchants and residents graciously accept the street people, but most do. Like the pigeons of Venice, they're a nuisance but a vital part of the scene.

"The street people are harmless," says Mosias, whose art supply store has weathered 30 years on Haight Street. "Some merchants try to blame them for bad business because it's easier than blaming themselves and the street people are an easy target. But this is their neighborhood, too. They just happen to live on the streets."

To many shopkeepers and residents, and even police, the street people are a reassurance that despite Reaganomics, the new conservatism and preppies, the Haight is still the same liberal haven for eccentrics it has always been.

A short, muttering man wanders into a Haight Street gift shop, studies a few bright cards and then wanders out. The sales clerk, Rette Thomas, watches and says softly, "I respect them and I'm very proud of the Haight-Ashbury for letting these people live here."

Like everyone else on the street, the two beat policemen who walk Haight Street from 3 to 11 p.m. know all the street people by name.

Sensitive to the role these gypsies play in the community, officer Ken Blevins, 31, tries to maintain a balance between laissez-faire and law enforcement. Blevins and his partner, Corbett Dickey, 24, average 10 arrests a week, occasionally for loitering or begging, but usually for public drinking.

"I could arrest my regulars every day of the week," Blevins said. "But I don't. I live in this neighborhood, too. I don't want the neighborhood characterized by a bunch of drunks. But these people add a lot of color to the street and I don't want to lose that."