President Biden will announce new steps on Tuesday to confront a staggering surge in coronavirus cases, including readying 1,000 military medical professionals to help at overburdened hospitals, setting up new federal testing sites, deploying hundreds of federal vaccinators and buying 500 million rapid tests to distribute free to the public.

The measures, outlined to reporters Monday night by two senior administration officials who spoke on condition of anonymity, come as coronavirus caseloads are rapidly rising around the country, particularly in the Northeast, fueled by the highly infectious new Omicron variant — just as Americans prepare to gather for Christmas.

The 500 million tests that the administration intends to purchase will not be available until January, the senior officials said, adding that the government intends to create a website where people can request that tests be sent to their homes, free of charge. It was not immediately clear where the tests would come from.