The Obama administration has poured billions of dollars into expanding the reach of the Internet, and nearly 98 percent of American homes now have access to some form of high-speed broadband. But tens of millions of people are still on the sidelines of the digital revolution.

“The job I’m trying to get now requires me to know how to operate a computer,” said Elmer Griffin, 70, a retired truck driver from Bessemer, Ala., who was recently rejected for a job at an auto-parts store because he was unable to use the computer to check the inventory. “I wish I knew how, I really do. People don’t even want to talk to you if you don’t know how to use the Internet.”

Mr. Griffin is among the roughly 20 percent of American adults who do not use the Internet at home, work and school, or by mobile device, a figure essentially unchanged since Barack Obama took office as president in 2009 and initiated a $7 billion effort to expand access, chiefly through grants to build wired and wireless systems in neglected areas of the country.

Administration officials and policy experts say they are increasingly concerned that a significant portion of the population, around 60 million people, is shut off from jobs, government services, health care and education, and that the social and economic effects of that gap are looming larger. Persistent digital inequality — caused by the inability to afford Internet service, lack of interest or a lack of computer literacy — is also deepening racial and economic disparities in the United States, experts say.