What if the very thing that is often viewed as one of the United States’ sources of dynamism — flexible labor markets — is the driving force behind the economy’s greatest weakness: millions of people who are neither working nor looking for a job?

That is a provocative idea that Obama administration economists explore in a new report looking at one of the crucial flaws in what on the surface is a healthy job market. Even as the unemployment rate has fallen to 4.7 percent — low by historical standards — millions of working-age Americans have pulled out of the labor market entirely. They neither work nor count as unemployed.

These missing workers are predominately less educated men, and their numbers have been mounting for decades. The White House Council of Economic Advisers calculates that in 1964, 97 percent of men with a high school degree or less in the so-called prime-age working years of 25 to 54 were working or seeking work. That is now down to 83 percent.

In the United States, there is less standing in the way between an employer who wants to hire someone and a person who wants to work than in most Western European countries or Japan.