In states judged to be doing well enough to enter the first phase, schools would remain closed and people would still be urged to avoid socializing in groups of more than 10. But some large public places — including restaurants, movie theaters, sporting venues and places of worship — would be allowed to operate under strict physical distancing protocols. Elective surgeries could resume and gyms could reopen as long as they maintained physical distancing. Bars would remain closed.

In the second phase, which could begin after another two-week decline in the number of coronavirus cases, schools could reopen and people would be advised to avoid social gatherings of more than 50.

By the third phase, states with no evidence of a resurgence of infections would be able to resume unrestricted staffing of work sites, visits to hospitals and nursing homes, and the operation of large venues under limited social distancing protocols. Bars could reopen with increased standing room.

In addition to the guidelines, the Centers for Disease Control and Prevention are expected to soon announce that the agency will hire hundreds of people to perform contact tracing as part of the push to allow the country to go back to work and school, according to a federal official.

Under the plan, the official said that the federal government would also help states pay for more medical personnel to help track the spread of the coronavirus by contacting people who test positive to see who they had contact with three or four days before they started showing symptoms. “If we see a hot spot developing, we’ve learned a lot,” Mr. Trump said. “We’ll be able to suppress it, whack it.”

Many public health experts have cautioned that hiring several hundred people for the entire country will be nowhere near enough to keep track of the virus as it spreads. Dr. Thomas R. Frieden, a former C.D.C. director, said there were estimates that the country would need to hire as many as 300,000 such workers.

The federal guidelines outline much the same strategy that a number of local and state governments have already adopted in anticipation of the day when social restrictions are eased, interviews with health officials in a half-dozen states show.