“We had the responsibility for closing states down, essentially,” Mr. Wolf said, referring to other governors wrestling with the matter. “We also have the responsibility — the feet on the ground here, the people who know best what’s going on in our state — to figure out how we’re going to reopen.”

The plans in the Northeast will be developed by an improvised think-tank-like team with three representatives — the chief of staff, an economic development expert and a health expert — from each state. The governors who formed the coalition, which also includes Connecticut, Delaware, Massachusetts, New Jersey, New York and Rhode Island, said the group would create “a fully integrated regional framework” while weighing economic, scientific and social data.

From the beginning, there has been no central playbook for how to handle the coronavirus in the United States.

Some states, like California, shut down early and entirely. Others, like Florida and Texas, issued piecemeal orders for residents to stay home, first at the city and county level, and later statewide. A small number of more rural states, including Arkansas, Iowa, Nebraska, North Dakota and South Dakota, have yet to adopt stay-at-home orders, deciding instead to close businesses and appeal to residents’ judgment.

It is possible that the reopening of America could be just as ad hoc.

One model by the Institute for Health Metrics and Evaluation at the University of Washington, which has been cited by the White House, predicts that states that were slower to adopt the most stringent social distancing orders will see the worst of the crisis last through the beginning of June, a month longer than states that took early action.

“We’re seeing right now two different Americas,” said Ali Mokdad, a public health expert at the University of Washington who worked on forecasting. “When we talk as a country about needing to go back to business, certain states are ready theoretically as of May, but many aren’t as of June.”

As long as the virus is active anywhere, he said, there will be risks. “We are a mobile society and we travel a lot,” he said. “That’s the problem.”