NEW YORK — A period of relative calm on Wall Street ended in the last hour of trading today as stocks tumbled amid growing investor anxiety about the government's key November employment report.

The major indexes each fell more than 3 percent, including the Dow Jones industrial average, which dropped more than 300 points.

It was clear that investors were worrying that Friday's employment report would show a further deterioration in the job market. Employers have cut 1.2 million jobs this year through October, leaving the unemployment rate at a 14-year high of 6.5 percent.

Economists expect the Labor Department will report Friday that the rate increased to 6.8 percent in November and that companies cut another 320,000 jobs.

The late-session decline followed a decent run for stocks, which have closed higher in seven of the last eight sessions. It also came as the heads of the Detroit automakers appeared before Congress with hopes of persuading skeptical lawmakers to save their troubled industry. While the market expects the Detroit companies will be able to win some aid from Capitol Hill, support for the troubled companies wasn't assured.