WASHINGTON — Hundreds of thousands of people could soon lose food stamps as states reimpose time limits and work requirements that were suspended in recent years because of high unemployment, state officials and advocates for the poor said Friday.

Liberal groups said that many unemployed childless adults with low incomes could be cut off, starting this month, as a result of the time limits, which date back to the 1996 welfare law.

About 45 million people receive benefits in the food stamp program, now known as the Supplemental Nutrition Assistance Program, or SNAP. The Center on Budget and Policy Priorities, a liberal-leaning research and advocacy group, estimates that 500,000 to a million people will lose benefits this year.

The federal Food and Nutrition Service said many adults would need to take steps to meet work requirements or risk losing aid.