Fewer new businesses are getting off the ground in the U.S., available data suggest, a development that could cloud the prospects for job growth and innovation.

In the early months of the economic recovery, start-ups of job-creating companies have failed to keep pace with closings, and even those concerns that do get launched are hiring less than in the past. The number of companies with at least one employee fell by 100,000, or 2%, in the year that ended March 31, the Labor Department reported Thursday.

That...