Nobel laureate Richard Thaler wants to mesh 401(k) plans with Social Security benefits to help Americans simplify what is perhaps their most daunting and complex financial issue: drawing down retirement assets.

Mr. Thaler, who won the Nobel Prize in 2017 for his work on behavioral economics, said Americans should be allowed to contribute more into Social Security using a portion of their 401(k) benefits when they retire, which would increase the size of their monthly Social Security checks.

Allowing retirees to send up to perhaps $100,000 or $250,000 of their 401(k) balances to the Social Security Administration would deliver an inflation-adjusted annuity, guaranteed by the federal government at fair actuarial value over a retiree's lifetime — which companies in the private sector are loath to do, said Mr. Thaler, a professor of behavioral science and economics at the University of Chicago Booth School of Business.