The underlying problem, progressive economists and advocates for poor people say, is that the work requirements do not actually work, and few studies examine how to make them more effective.

Welfare recipients forced off the rolls by the 1996 law were only slightly more likely to get jobs than people who continued to receive benefits, and the incentive effects of the work requirement dissipated over time, according to a University of Chicago study in 2005.

“This all starts with the assumption that if you make people miserable enough, they will go out and find a job,” said LaDonna Pavetti, the vice president for family income support policy at the Center on Budget and Policy Priorities, a left-leaning think tank in Washington.

“The reality of people’s lives is much more complicated than that. It doesn’t take into account the barriers they face, but also the color of their skin, their prison record, and barriers like education, transportation, child care and the lack of good-paying jobs where they live,” she said. “None of these proposals have adequate resources to deal with any of those barriers.”

Mr. Bremberg, in an interview, said: “The goal is not to kick people off support programs. The goal is to get people into productive jobs.” He added that the president’s main objective was matching millions of able-bodied potential workers with millions of jobs that remain unfilled because of the shortage of suitable workers.

Still, the resources dedicated to increased work force development in Mr. Trump’s 2019 budget, released last month, are relatively modest compared with the deep cuts proposed for safety net programs. And the work requirements come in addition to the administration’s proposal to drastically cut domestic spending, including a plan to trim food aid by $213 billion over the next decade.

The Department of Housing and Urban Development, which is slated to absorb a $6 billion cut next year under the president’s budget, has begun looking at ways to expand a small demonstration project centered on work requirements into its public housing and voucher programs.