WASHINGTON — Philanthropist Melinda Gates announced a $34.8-million award to high-performing community colleges Tuesday at the White House’s first summit on community colleges, an effort by the Obama administration to promote the schools as a path to jobs for middle-class Americans.

“In this country hard work is supposed to pay off,” Melinda Gates said. “And I’m excited to see so many people come here today to guarantee that it pays off for young adults who attend community colleges.”

President Barack Obama praised community colleges for opening doors to workers in need of low-cost degrees and announced new funding to increase graduation and job-placement rates.

Second lady Jill Biden, a community college instructor, called community colleges “America’s best-kept secrets.” She has been appointed by the administration to help America regain its standing as the nation with the highest proportion of college degrees by 2020.

Biden, who holds a doctorate in education, said community colleges are uniquely positioned to be a link between business needs and untrained job seekers.

“They are equipping Americans with the skills and expertise that are relevant to the emerging jobs of the future, ” Biden said. “They are opening doors for the middle class at a time when the middle class has seen so many doors closed to them. ”

The summit highlighted the administration’s endorsement of public community colleges and its efforts to regulate private for-profit colleges, such as the University of Phoenix. Both brands are competing to enroll the same pool of low-income students, but the Department of Education and Democrats in Congress say for-profit colleges are in the education business for the wrong reasons, creating more student debt than trained graduates.

The Department of Education has plans to require for-profit colleges to prove their students are placed in jobs when they graduate, so students are more likely to pay back their student loans. Dropouts frequently don’t repay their loans.

Many Republicans disagree with the plan. At a committee hearing Thursday, Sen. Mike Enzi, R-Wyo., accused Democrats of examining for-profit colleges in a vacuum and of glossing over the problems at community colleges.

In fact, a recently released study, based on data from the Department of Education, reported that for-profit colleges graduate 58 percent of their students while community colleges graduate only 20 percent.

Jean Norris, managing partner of Norton Norris Incorporated, which conducted the study, said the Government Accountability Office released only negative information about for-profit colleges without looking at community colleges.

“What’s most interesting to me is why there is this singular focus on career [for-profit] colleges and that community colleges are our only option,” Norris said. “I’m afraid people aren’t informed enough to know that community colleges are subsidized by our taxes. You know why career colleges cost so much? Because they don’t get the subsidies.”

The debate kept its divisive flavor at the White House summit. Obama criticized the Republicans’ “Pledge to America” for eliminating financial aid to more than 8 million college students and cutting the education budget by 20 percent.

“Think about it, China isn’t slashing education by 20 percent right now. India is not slashing education by 20 percent,” Obama said. “We are in a fight for the future, a fight that depends on education.”

Two funding programs were announced at the summit. “Completion by Design” will allocate $34.8 million from the Bill and Melinda Gates Foundation to community colleges that show high graduation and job placement rates. “Skills for America’s Future,” an initiative of the Aspen Institute in partnership with the Pritzker Traubert Family Foundation, plans to connect employers and union leaders with community colleges to identify job skills in demand.