WASHINGTON - In another sign that the Department of Agriculture is embracing sustainable food, the agency last week unveiled expanded plans for a People's Garden that will encompass the entire six-acre grounds of the Whitten Building, the department's neoclassic marble headquarters on the Mall.

The plans, announced at the agency's Earth Day celebrations, include a 1,300-square-foot organic vegetable garden - slightly larger than the one at the White House - as well as ornamental flower gardens and bioswales, or mini-wetlands designed to reduce pollution and surface water runoff. The grounds now are landscaped with grass, flower borders, and trees planted to honor a person or mark an event.

The garden will be tended by workers from Melwood, a Maryland nonprofit organization that employs developmentally disabled adults. USDA staff will be encouraged and permitted to help.

Secretary Tom Vilsack, an avid runner, came up with the idea for the garden during one of his daily runs around the Mall. He noticed tourists stopping to look at the trees and their dedication plaques. A thriving garden, he thought, would be a better way to communicate the agency's mission of sustainability and the importance of fresh fruits and vegetables, a cornerstone of the agency's push to improve school nutrition and reduce childhood obesity.

Initial plans were announced at a groundbreaking in February on Abraham Lincoln's birthday. Lincoln founded the Department of Agriculture in 1862, calling it the People's Department, hence the name People's Garden.

Originally, Vilsack, 58, envisioned a vegetable garden only half the size and a goal to have at least some type of garden - even if just a window box - at every USDA facility. But in an interview at his office, which overlooks the scrubby lawn, Vilsack said the positive public response to the idea and a March meeting with horticulture and garden groups persuaded him to broaden the plan. The garden now will encompass all of the agency's property on the Mall, and the department will work with organizations across the country to encourage individuals, schools, and communities to establish gardens.

"If we can get people to focus on fruits and vegetables and more healthy foods, we'll be better in terms of our health-care situation," Vilsack said.

The organic vegetable garden will feature a rotation of crops, beginning with cool-weather plants such as field peas, lettuce, spinach, and kale. As summer approaches, tomatoes, peppers, squash, and herbs, among other things, will be planted.

There will also be a three sisters garden, a traditional American Indian planting method in which corn, pole beans, and squash are grown together. The beans fix nitrogen, a fertilizer, in the soil and use the cornstalks as natural poles to climb. Squash has big leaves that shade the soil, keeping it moist and blocking light that would encourage weeds.

All of the vegetables produced will be donated to a local food bank. But the garden's primary role is to be an educational tool. Gardeners will work toward winning organic certification; signs and possibly a video at the USDA visitors' center will explain the process and benefits of organic agriculture. The vegetables will be grown in three ways: in the ground (the soil has been tested several times and contains no chemical residues), in raised beds, and in containers. The goal is to illustrate the many ways to grow food, dispelling the notion that gardeners need large plots of land.

The emphasis on gardening might surprise some sustainable-agriculture advocates who initially greeted Vilsack's appointment with skepticism. A former governor of Iowa, Vilsack had close ties to conventional farmers and ranchers and had supported biotechnology and ethanol. But in his first 91 days, the secretary has made concerted efforts to win food advocates' trust. He has met with progressive farm groups and food policy organizations and watched a screening of Food, Inc., a searing indictment of the industrial food system, with authors Eric Schlosser and Michael Pollan, two leaders of the sustainable-food movement. One of Vilsack's standard lines is, "If I had to summarize the vision I have for this department in one word, it would be sustainable."

The new garden has provided another chance to include new voices, Vilsack said. In March, he convened a one-day meeting in Washington at which 47 gardening and horticulture organizations, including the Rodale Institute, Seed Savers, and the American Community Gardeners Association, offered feedback on the project and brainstormed ways to spread the message to schools, churches, and communities.

"I kept having to pinch myself in this meeting," said Rose Hayden-Smith, a historian and food systems educator at the University of California. "We're not the kind of people who have been invited to Washington, D.C., before."

This is not the first time the federal government has encouraged Americans to plant gardens. During World War I, the Department of the Interior launched a Liberty Garden program, and the Federal Bureau of Education established the United States School Garden Army, an unprecedented effort to make agricultural education a formal part of the public school curriculum.

Vilsack said the struggling economy, concerns about climate change, and rising obesity rates mean the time is right for that to change. But it's also clear that Vilsack's exposure to sustainable-food advocates and ideas has turned him into a bit of a foodie himself. "I don't care what anybody says: Nothing is better than a tomato you grow," he said. "There's something about it that's different than a tomato you can buy. It's a great thing."