WASHINGTON — The Trump administration is taking a step toward tightening work requirements in the food-stamp program, with a focus on high-unemployment areas that have been exempted from those rules since the recession. On Friday, the Department of Agriculture will begin soliciting public comment on work requirements, the first step toward changing those rules, USDA administrator Brandon Lipps said in a conference call with reporters Thursday. The agency is not advancing any changes to the Supplemental Nutrition Assistance Program — better known as “food stamps” — at this time, Lipps said.