While the organic garden will provide food for the first family’s meals and formal dinners, its most important role, Mrs. Obama said, will be to educate children about healthful, locally grown fruit and vegetables at a time when obesity and diabetes have become a national concern.

“My hope,” the first lady said in an interview in her East Wing office, “is that through children, they will begin to educate their families and that will, in turn, begin to educate our communities.”

Twenty-three fifth graders from Bancroft Elementary School in Washington will help her dig up the soil for the 1,100-square-foot plot, in a spot visible to passers-by on E Street. (It is just below the Obama girls’ swing set.)

Students from the school, which has had a garden since 2001, will also help plant, harvest and cook the vegetables, berries and herbs. Virtually the entire Obama family, including the president, will pull weeds, “whether they like it or not,” Mrs. Obama said with a laugh. “Now Grandma, my mom, I don’t know.” Her mother, she said, will probably sit back and say: “Isn’t that lovely. You missed a spot.”

Whether there would be a White House garden had become more than a matter of landscaping. The question had taken on political and environmental symbolism, with the Obamas lobbied for months by advocates who believe that growing more food locally, and organically, can lead to more healthful eating and reduce reliance on huge industrial farms that use more oil for transportation and chemicals for fertilizer.

Then, too, promoting healthful eating has become an important part of Mrs. Obama’s own agenda.

The first lady, who said that she had never had a vegetable garden, recalled that the idea for this one came from her experiences as a working mother trying to feed her daughters, Malia and Sasha, a good diet. Eating out three times a week, ordering a pizza, having a sandwich for dinner all took their toll in added weight on the girls, whose pediatrician told Mrs. Obama that she needed to be thinking about nutrition.

“He raised a flag for us,” she said, and within months the girls had lost weight.

Dan Barber, an owner of Blue Hill at Stone Barns, an organic restaurant in Pocantico Hills, N.Y., that grows many of its own ingredients, said: “The power of Michelle Obama and the garden can create a very powerful message about eating healthy and more delicious food. I don’t think it’s a stretch to say it could translate into real change.”

While the Clintons grew some vegetables in pots on the White House roof, the Obamas’ garden will far transcend that, with 55 varieties of vegetables — from a wish list of the kitchen staff — grown from organic seedlings started at the Executive Mansion’s greenhouses.

The Obamas will feed their love of Mexican food with cilantro, tomatillos and hot peppers. Lettuces will include red romaine, green oak leaf, butterhead, red leaf and galactic. There will be spinach, chard, collards and black kale. For desserts, there will be a patch of berries. And herbs will include some more unusual varieties, like anise hyssop and Thai basil. A White House carpenter, Charlie Brandts, who is a beekeeper, will tend two hives for honey.

The total cost of seeds, mulch and so forth is $200, said Sam Kass, an assistant White House chef, who prepared healthful meals for the Obama family in Chicago and is an advocate of local food. Mr. Kass will oversee the garden.

The plots will be in raised beds fertilized with White House compost, crab meal from the Chesapeake Bay, lime and green sand. Ladybugs and praying mantises will help control harmful bugs.

Cristeta Comerford, the White House’s executive chef, said she was eager to plan menus around the garden, and Bill Yosses, the pastry chef, said he was looking forward to berry season.

The White House grounds crew and the kitchen staff will do most of the work, but other White House staff members have volunteered.

So have the fifth graders from Bancroft. “There’s nothing really cooler,” Mrs. Obama said, “than coming to the White House and harvesting some of the vegetables and being in the kitchen with Cris and Sam and Bill, and cutting and cooking and actually experiencing the joys of your work.”

For children, she said, food is all about taste, and fresh and local food tastes better.

“A real delicious heirloom tomato is one of the sweetest things that you’ll ever eat,” she said. “And my children know the difference, and that’s how I’ve been able to get them to try different things.

“I wanted to be able to bring what I learned to a broader base of people. And what better way to do it than to plant a vegetable garden in the South Lawn of the White House?”

For urban dwellers who have no backyards, the country’s one million community gardens can also play an important role, Mrs. Obama said.

But the first lady emphasized that she did not want people to feel guilty if they did not have the time for a garden: there are still many changes they can make.

“You can begin in your own cupboard,” she said, “by eliminating processed food, trying to cook a meal a little more often, trying to incorporate more fruits and vegetables.” " Marian Burros, NY Times