WASHINGTON—America’s employers unleashed a burst of hiring in March, adding 916,000 jobs in a sign that a sustained recovery from the pandemic recession is taking hold as businesses increasingly reopen. The March increase—the most since August—was nearly double February’s gain of 468,000, the Labor Department said Friday. The unemployment rate declined from 6.2 percent to 6 percent. Even with last month’s robust increase, the economy remains more than 8 million jobs short of the number it had before the pandemic erupted a little over a year ago. But with the recovery widely expected to strengthen, many forecasters predict enough hiring in the coming months to recover nearly all those lost jobs by year’s end. Regaining all those jobs, though, will be a daunting task. “We can rejoice in these numbers, but we still have a lot of work to do,” said Jane Oates, president of WorkingNation and a former Labor …