WASHINGTON — The Department of Agriculture, brushing aside tens of thousands of protest letters, gave final approval on Wednesday to a new rule that would remove nearly 755,000 people from the federal food-stamp program.

The rule, which was proposed in February, makes it more difficult for states to allow able-bodied adults without children to receive food assistance for more than three months out of a 36-month period without working. More than 140,000 public comments flooded in before the department’s comment period closed in April, and they were overwhelmingly negative.

But the department was unmoved from its position that the granting of state waivers needed to be stricter because the economy had improved under the Trump administration and assistance to unemployed, able-bodied adults was no longer necessary in a strong job market.

“Government can be a powerful force for good, but government dependency has never been the American dream,” Sonny Perdue, the agriculture secretary, said. “We need to encourage people by giving them a helping hand but not allowing it to become an indefinitely giving hand.”

But anti-poverty groups said the administration’s focus on the unemployment rate was misleading.

“The overall unemployment rate is really a measure of the whole labor market and not people without a high school diploma who are incredibly poor and may lack transportation,” said Stacey Dean, the vice president of food assistance policy at the liberal Center on Budget and Policy Priorities. “We’re talking about a different group who just face a very different labor market.”

The rule is the first of three department efforts to scale back the food stamps program. Mr. Perdue said the rules were an effort to encourage self-sufficiency, save taxpayer money and ensure that only those who truly need benefits receive them.

The department has also proposed a rule that would close what it calls a loophole that allows people with incomes up to 200 percent of the poverty level — about $50,000 for a family of four — to receive food stamps. It also wants to prevent households with more than $2,250 in assets, or $3,500 for a household with a disabled adult, from receiving food stamps. That would strip nearly 3 million people of their benefits, and nearly 1 million children would lose automatic eligibility for free or reduced-price school meals. The proposal received 75,000 public comments, which were overwhelmingly negative.

Another proposal would cut $4.5 billion from the program over five years by adjusting eligibility formulas, affecting one in five struggling families. That one received 90,000 comments.

The Supplemental Nutrition Assistance Program, commonly known as the food stamps program, has two sets of work requirements for participants, one for parents and another for able-bodied adults without children. Wednesday’s rule makes it more difficult for states to waive the time limit for the second set of work requirements.

States have typically waived the three-month time limit for one or two years in areas that have a lack of sufficient jobs or high unemployment rates. Every state except Delaware has used the waiver in the past 23 years. After the 2008 recession, the time limit was suspended in areas representing nearly 90 percent of the population.

Ms. Dean said the final rule was actually made tougher than the initial proposal, because “it makes it much harder for states with high unemployment to qualify for waivers during a national recession.”

But Robert Rector, a senior research fellow at the conservative Heritage Foundation, said the incentives in the old waiver system encouraged states to petition the federal government for their citizens.

“States do not pay one dime in the cost of food stamps,” he said. “They didn’t even pay for most of the administrative costs. Therefore we should have a federal work requirements on a federally funded program.”

Without a waiver, able-bodied adults without children must work or participate in a work program for 20 hours or more a week to qualify for food stamps. That requirement can be difficult for people who are already homeless or have significant health issues, some poverty experts said, especially for low-wage workers who often are not offered 20 hours a week of steady work.

If the Agriculture Department finalizes the other two rules, nearly 4 million people would lose food assistance and nearly one million school children would lose access to free or reduced price school meals, according to a new study by the Urban Institute.

Representative Marcia L. Fudge, Democrat of Ohio and chairwoman of the House Agriculture Committee’s subcommittee on nutrition, said in a statement that instead of “considering hungry individuals and their unique struggles and needs, the department has chosen to paint them with the broadest brush, demonizing them as lazy and undeserving.”