Ms. Sanders also said the citizenship question had “been included in every census since 1965, with the exception of 2010, when it was removed.”

In fact, various citizenship questions have appeared in many censuses since 1850, especially during periods of high immigration. But it was dropped from the 1960 general census (there was no census in 1965) and relegated in 1970 to a longer list of questions that were asked of a small minority of residents. After 2000, the question was asked only on the American Community Survey, a separate mandatory poll of a fraction of the population that is conducted more frequently than the census.

Critics noted that the citizenship question was added at the last minute — the deadline for proposing new questions for the 2020 head count is April 1 — and that it sidestepped the years of vetting undergone by every other question that will be asked. This month, they added, President Trump’s re-election campaign used the addition of a citizenship question in an emailed fund-raising appeal.

Mr. Schneiderman, the New York attorney general, said that adding the question was a “reckless decision to suddenly abandon nearly 70 years of practice.” He argued that the move “will create an environment of fear and distrust in immigrant communities that would make impossible both an accurate census and the fair distribution of federal tax dollars.”

In a seven-page announcement released late Monday, Wilbur L. Ross Jr., the secretary of commerce, foresaw those concerns, and sought to allay them. Decades of experience with citizenship questions on earlier censuses and other surveys, he stated, indicate that including it on the 2020 form would not deter people from volunteering to be counted. And he noted that other democracies, from Australia to the United Kingdom, routinely ask about citizenship in their head counts without any difficulty.

Mr. Ross, whose department oversees the Census Bureau, acknowledged that both outside experts and leaders within the bureau had been opposed to the change. But he said that “neither the Census Bureau nor the concerned stakeholders could document that the response rate would in fact decline materially.”