WASHINGTON — U.S. hiring slowed to a near-standstill in May, sowing doubts about the economy’s health and complicating the Federal Reserve’s efforts to raise interest rates.

While unemployment slid from 5 percent to 4.7 percent, the lowest since November 2007, the rate fell for a troubling reason: Nearly a half-million jobless Americans stopped looking for work and so were no longer counted as unemployed.

Employers added just 38,000 jobs in May, the fewest in over five years.

Less-educated workers bore the brunt of the hiring slump, with a quarter-million high school dropouts losing their jobs in May. That has perpetuated a long-term trend toward a two-tiered job market, with college-educated adults more likely to be employed and earning steady raises.

“The shockingly low payrolls gain in May provides further evidence that the economy is showing clear signs of slowing,” said Laura Rosner, an economist at BNP Paribas.