WASHINGTON — As the Census Bureau finalizes the questions for the 2020 census, key voices in the Trump administration are pressing for surveyors to ask one critical question: Are you a United States citizen?

Advocates of the so-called citizenship question say it is merely clerical, an effort to ascertain how many noncitizens reside in the United States. But the question would have broad ramifications, not only for the politics of redistricting that will emerge from the census but for an issue that goes beyond partisanship: public health.

The fear is that immigrants — even those in the country legally — will not participate in any government-sponsored questionnaire that could expose them, their family members or friends to deportation. But low response rates from any demographic group would undermine the validity of the next decade of health statistics and programs, health experts warn. Scientists use census data to understand the distribution of health conditions across the United States population. In turn, officials use the data to target interventions and distribute federal funding.

“Data is the lifeblood of public health; it needs to be transparent and objective,” said Edward L. Hunter, the former chief of the Centers for Disease Control and Prevention’s Washington office and now the president of the de Beaumont Foundation, which focuses on public health. “The census will have cascading effects upon every rate, every percentage, every trend we monitor over time. It’s very unsettling for people who need to use that data.”