Image Gary Hirshberg of Stonyfield Farm said of the organic food movement: This has never been just about business. We are here to change the world. Credit... J. Emilio Flores for The New York Times

In addition, some sustainable-farm advocates who have worked on these issues for decades in Washington are chafing at the idea of celebrity activists swooping into town.

Ferd Hoefner, policy director of the Sustainable Agriculture Coalition, says that during the Carter administration he fought to get $5 million in federal money to promote farmers’ markets (about the same as allocated last year).

While he acknowledges that it has been an uphill fight, Mr. Hoefner said the activists had made major strides in recent years, winning more federal dollars for organic research and to help farmers convert to organic methods and add value to their operations by, for example, converting to grass-fed beef. As part of the economic stimulus plan, the Agriculture Department also plans to award $250 million in loan guarantees, spread over the next two years, for local and regional food networks, he said.

Mr. Hoefner said he was impressed by the number of people who rallied for a White House garden. “We just want to make sure that interest in that symbolic action can be channeled into some of the more difficult policy challenges,” he said.

Senator Tom Harkin, Democrat of Iowa and chairman of the Senate Agriculture Committee, welcomes newcomers to the cause but cautions that farm policy “does not have sharp turns.”

Mr. Harkin has spent years trying to increase federal dollars for child nutrition and for conservation programs that reward farmers for protecting the environment, relatively small programs that he says can expand under the Obama administration.