The initiative, known as United We Serve, was announced by President Barack Obama in a video message last week.
The president is urging people to help in the nation's economic recovery by volunteering at schools and hospitals and pitching in on community needs ranging from tutoring to trash pickup.
Michelle Obama put the idea into action by joining California first lady Maria Shriver and local volunteers at Bret Harte Elementary School in San Francisco, where the playground is being refurbished to include an edible garden with a farmers market stand where kids and seniors can sell vegetables to raise money for the school.
Later, the first lady is scheduled to speak at the 2009 National Conference on Volunteering and Service.
A number of other people are also set to speak, including Gov. Arnold Schwarzenegger.
Earlier, a volunteer driver from the nonprofit Disabled American Veterans participated in the United We Serve program by transporting Veterans Affairs Secretary Eric Shinseki and two Vietnam-era veterans through commuter traffic to a VA hospital in Washington.
Shinseki said he was amused by the advice the veterans gave the driver to quickly get to their appointments.
"Except for them, we'd still be in traffic," Shinseki told staff members at the hospital after the ride.
More than 80,000 people donated time last year helping with VA-related programs, but Shinseki said there's concern that there's been a decline in the number of volunteers.
Other senior VA officials volunteered at homeless shelters and in other ways.
Tammy Duckworth, a VA assistant secretary who lost both her legs and partial use of one arm in an attack in Iraq in 2004, recalled a fellow veteran offering to wash her hair when she was injured and another volunteer pulling up a blanket for her when she was on a gurney in a hospital hall and unable to move her arms.
"Sometimes, it's the smallest gesture that makes the difference to these vets," Duckworth said.
Other officials promoting the event included Attorney General Eric H. Holder Jr., who was to play basketball and talk with young people at the Police Athletic League in Philadelphia.
Commerce Secretary Gary Locke was visiting La Mesita Homeless Shelter for Families in Mesa, Ariz. to read to children and serve lunch at the child care center.
Housing Secretary Shaun Donovan was set to help rebuild a home in New Orleans.
United We Serve is led by the government-run Corporation for National and Community Service.