SAN FRANCISCO – For generations, the lawn at Civic Center Plaza was a lush, quarter-acre welcome mat outside City Hall, and a frequent staging ground for demonstrations.

But the grass has been torn out and replaced by tomato plants, spinach, beans and squash – an officially sanctioned and very organic protest against a culture of mediocre, unhealthy food.

The Victory Garden, as it is known, is the centerpiece of a food festival scheduled for Labor Day weekend that is intended to underscore the connection between planet and plate.

In the foggy summer weeks between July 1, when the turf was ripped up, and Labor Day, it is a living billboard for urban agriculture. Tourists and political gadflies, office workers and the homeless stroll the garden each day; volunteers hover nearby, ready to dish up information and shoo away squirrels.

“We’ve reached critical mass in the media,” says Anya Fernald, executive director of Slow Food Nation ’08, which organized and paid for the urban garden. “That level of critical mass has made it more acceptable to do the outrageous, and this is outrageous. We’ve just planted a farm in front of the mayor’s office!”

Touchy about his image as one of “these nutty mayors,” as he put it, Mayor Gavin Newsom denies there is any hippie plantation outside his office.

“Not everyone gets it yet. There have been some folks who criticize this as if we are building some farm out in City Hall,” he said.

Newsom has planted the seeds of a run for California governor, and, eyeing conservative voters in California’s real farm belt, doesn’t want to appear too crunchy.

But the mayor’s office approved of replacing lawn with lettuce, and Newsom said he has watched enthusiastically as “this victory garden” has sprouted.

“I have gotten to enjoy this the last few weeks right there – my office is literally right there, the window with those shades open – and every day I have been peeking out and looking at the progress,” he said. “I’m just like a kid, I’m so excited about this, so proud about this.”

Snap peas, broccoli, leeks, eggplant, pumpkins and peppers are flourishing in City Hall’s front yard, a bounty meant to peak for the festival. After the last speech, it will be harvested and donated to the San Francisco Food Bank for distribution to the needy.

To the mayor, the garden embodies a movement toward healthier foods that is a natural policy companion piece to his push for universal health care. “What we’re trying to do is move from access to investing in people’s health, not treating people when they are sick,” he said. “That’s what, to me, this whole movement is about.”

“This whole movement,” it turns out, includes a whole buffet of issues, from protecting workers’ and growers’ rights; to banishing pesticides and other chemicals; to ensuring rich and poor have equal access to good food.

To John Bela, who designed and managed the garden, it’s also about growing food closer to home.

“In San Francisco, we’re making the big, visible, symbolic gesture here, in an effort to bootstrap urban gardening in the Bay Area and look at the role of urban farming in creating a sustainable food system,” he said.

Fernald practically has to gulp for air as she rushes to tick off the issues driving “the movement.” “Concern about oil, concern about health, concern about childhood diabetes, obesity,” she said.

The garden is also a bridge to history. During World War II, City Hall’s lawns were ripped up and replaced with vegetable plants meant to ease produce shortages. Thousands thronged to a Victory Garden Fair in the park in June 1943.

Sixty-five years later, organizers are predicting as many as 50,000 people will descend on the City Hall area for the Slow Food Nation festival – what they are calling “the largest celebration of American food in history.”

It will graft a political rally onto the mother of all farmer’s markets. There will be seminars, chef demonstrations, produce spilling from crates, workshops, films, exhibits, music, and of course, tastings.

Bela and other organizers are uncertain what will happen to the garden after the festival, but they are almost certain it will not stay at City Hall. The soil and some other materials might be recycled and used at a garden in another city park, they said.

One recent day, it drizzled on the garden as the San Francisco Bicycle Coalition massed on the steps of City Hall and a few homeless people dozed through the protesters’ chants.

The homeless are a permanent fixture in San Francisco, and some seem to live near the garden.

Although the garden has a permanent security presence, Bela said he is untroubled by the prospect of a hungry person picking the occasional radish out of the garden.

“If people want to eat out of the garden, and they need to eat a piece of lettuce, that’s fine with me,” he said. “It’s good, organic food. That’s the least of my concerns.”