WASHINGTON — The American government paid $20.2 million in Social Security benefits to more than 130 United States residents linked to Nazi atrocities over the course of more than a half-century, with some of the payments made as recently as this year, according to a federal investigation.

The millions of dollars paid out, a total far higher than officials had previously believed, indicate the ease with which thousands of former Nazis managed to settle into new lives in the United States with little scrutiny after the end of World War II.

A report due to be released this week by the Social Security Administration’s inspector general concludes that virtually all of the payments were proper under policies in place at the time, and that federal officials did not have the legal authority to prohibit benefits until a Nazi suspect was deported, according to officials briefed on the report. The officials spoke on the condition of anonymity because the report has not yet been made public.

In the 1960s and 1970s, as dozens of aging former Nazis in the United States were beginning to collect Social Security benefits, there was little investigation by federal authorities into possible links of immigrants to atrocities committed in wartime Germany.