WASHINGTON — The number of Americans seeking unemployment pay plummeted last week to seasonally adjusted 339,000, the lowest level in more than four years. The sharp drop, if sustained, could signal a stronger job market.

The Labor Department said Thursday that weekly applications fell by 30,000 to the fewest since February 2008. The four-week average, a less volatile measure, dropped by 11,500 to 364,000, a six-month low.