With coronavirus infections soaring across the nation, federal health officials on Friday urged Americans in the most forceful language yet to take steps to protect themselves — starting with consistent, proper use of masks — and pressed local governments to adopt 10 public health measures deemed necessary to contain the pandemic.

The guidance reflected deep concern at the agency that the pandemic is spiraling further out of control and that many hospitals are reaching a breaking point, potentially disrupting health care across the country.

Agency officials have issued increasingly stark warnings in the waning weeks of the Trump administration, and President-elect Joseph R. Biden Jr. has promised a new national strategy to turn back the virus. On Thursday, Mr. Biden said he would call on Americans to wear facial coverings for 100 days.

FULLERTON, Calif. — The post-Thanksgiving rush for coronavirus testing is on: Pharmacies in the Southern California suburbs are advising customers lucky enough to score appointments that it could be four days before they receive results. In Chelsea, Mass., a line of people who hoped for testing, pelted by rain and wind, strung along an entire block early this week. In Atlanta, people have idled in cars, sometimes for hours, to get swabbed at drive-throughs.

Testing has long been one of the keys to controlling the spread of a virus that with the onset of winter is entering its most dangerous phase. Yet even as cases per capita have rocketed, securing a test has become enough of an ordeal that many people have been dissuaded from even trying.