Encore: Work that matters in the second half of life.

Barack Obama highlighted “seniors getting ready to retire” as a crucial source of new ideas “that could benefit millions of Americans if they’re given the chance to grow.”

The Democratic presidential candidate’s campaign also singled out Experience Corps as “a good model that should be expanded beyond reading and mentoring to other challenges on which national service will be focused.”

Obama’s call to action to meet the nation’s great challenges is notable for its inclusiveness – military as well as civilian, faith-based as well as secular and older as well as younger. He issued the call in Colorado Springs today and in Zanesville, Ohio earlier this week; his campaign provided additional details.

“Because the future of our nation depends on the soldier at Ft. Carson, but it also depends on the teacher in East L.A., the nurse in Appalachia, the after-school worker in New Orleans, the Peace Corps volunteer in Africa and the foreign service officer in Indonesia,” he said in Colorado. “Americans have shown that they want to step up. But we’re not keeping pace with the demand of those who want to serve, or leveraging that commitment to meet national challenges.”

Obama called for an expansion of AmeriCorps, the major national service program, from 75,000 positions to 250,000. He pledged to double the size of the Peace Corps, which is itself on a campaign to double the percentage of older volunteers.

Republican presidential candidate John McCain has also supported the expansion of AmeriCorps in the past. Campaigning recently in the “volunteer state” of Tennessee, McCain said, “My one job and my one accomplishment will be to inspire Americans to serve a cause greater than their self-interest. I will tell Americans of the beauty and the nobility of serving a cause greater than their self-interest.”

Obama’s campaign said the expansion of AmeriCorps would include the creation of five new “corps,” including a Clean Energy Corps and a Classroom Corps. The campaign said the Clean Energy Corps would enlist young people as well as veterans to clean polluted areas, help weatherize homes and gain job skills for the growing green economy. The Classroom Corps would enlist retired or mid-career engineers and scientists to help math and science teachers with mentoring, tutoring and tech support, and recruit civic, business and faith leaders to offer after-school and community-service opportunities.

“People of all ages, stations and skills will be asked to serve,” he said in Colorado.

Obama’s campaign said he would specifically “challenge boomers to help meet the challenges in our communities and our country.” Obama pledged to work to provide additional income security, including assistance with health coverage and other costs, for people who participate in citizen service.

Significantly, Obama endorsed social entrepreneurship as a significant public policy tool, calling for a Social Investment Fund Network to “invest in ideas that work; leverage private sector dollars to encourage innovation; and expand successful programs to scale.” Just as the Small Business Adminstration coordinates support for small companies, a new Social Entrepreneur Agency would muster federal support for small nonprofits, he said.

“The challenges we face today — from saving our planet to ending poverty — are simply too big for government to solve alone,” Obama said at the community center in eastern Ohio. “We need an all-hands-on-deck approach.”