Employers added fewer jobs in March than in any month in almost a year, a dark cloud after several months of slowly improving conditions in labor markets.

Just 88,000 jobs were created last month, far below February's 268,000 gain. The unemployment rate, derived from a separate survey, dropped to a four-year low of 7.6%. But the decline was prompted by nearly a half-million workers leaving the job market, not job growth.

Friday's...