HARRISBURG — The Wolf administration will begin its reopening experiment next week in large swaths of northern Pennsylvania, the first step in its tiered plan to gradually lift sweeping orders that have shut down nearly every aspect of daily life.

Gov. Tom Wolf on Friday announced that 24 northwestern and north-central counties can enter the “yellow” phase of his color-coded reopening plan next Friday, allowing many businesses to resume in-person operations and residents to freely leave their homes if they take precautions. The counties chosen have relatively low case counts and sufficient capacity for detection and treatment measures, Wolf said, and are largely less densely populated areas.

The Philadelphia region is expected to be among the last to reopen, and Wolf urged residents in areas still in the “red” phase to practice prevention measures to help speed the move to yellow.

But he tried to strike a positive note in his mid-afternoon briefing Friday, crediting the willingness of residents across the state to stay home with slowing the spread of the virus.

“We finally made it to the moment of starting to reopen our commonwealth, and it has been a tough time for everyone,” Wolf said. “Every Pennsylvanian should feel proud of the work we all did to flatten this curve, and every Pennsylvanian should take this moment to feel motivated by the success we have had.”

State officials also broadly outlined how they plan to ramp up testing and contact tracing to the levels needed to safely reopen the state. But the testing goal falls far below what most national experts say is needed, while the contact tracing plan lacked details about how many people the state will hire to do these crucial investigations.

The counties allowed to enter the yellow phase are Bradford, Cameron, Centre, Clarion, Clearfield, Clinton, Crawford, Elk, Erie, Forest, Jefferson, Lawrence, Lycoming, McKean, Mercer, Montour, Northumberland, Potter, Snyder, Sullivan, Tioga, Union, Venango, and Warren. Wolf did not provide a timeline for reopening other counties.

In Philadelphia, the virus is on a “very slow” decline, said Health Commissioner Thomas Farley. Like Wolf, he said residents could help hasten improvements by following social distancing measures.

Philadelphia reported 669 new confirmed cases, a number due in large part of a backlog at laboratories and also in part to expanded testing, and announced 31 additional deaths, bringing the city’s toll to 638. The city’s testing capacity is gradually increasing, Farley said, and an increasing number of laboratory results are coming in daily.

Pennsylvania announced 1,208 new cases of the coronavirus on Friday, for a total of 46,971 cases. Of those, 2,354 patients have died. As of Friday, 2,677 patients remain hospitalized statewide.

Hospitalizations in Philadelphia and its surrounding counties have remained about steady for the last week, Farley said. On Friday, 976 patients were hospitalized in Philadelphia, and 1,812 in all of Southeastern Pennsylvania.

Even as construction projects resumed and golf courses reopened on Friday, Mayor Jim Kenney urged residents to stay home and said he worried that another spike in cases could occur if people decide to disregard social distancing measures or not wear masks as the weather gets warmer.

“I know everybody’s got cabin fever and people want to get out, and they want to exercise and I totally get that,” he said. "If you can’t put a mask on, what are you saying about your attitude toward your fellow man and woman and your fellow citizens? So just put the mask on and stay six feet apart.”

Montgomery County officials, encouraging residents to walk in their own neighborhoods instead of crowding trails, created an interactive “low stress streets” portal to help residents find neighborhood areas near their homes where it may be easy to bike, run, and walk.

New Jersey Gov. Phil Murphy also urged caution as his state prepared to reopen parks and golf courses this weekend. Ventnor said it would reopen beaches next Friday but keep the Boardwalk closed, and Cape May will partially reopen its beaches, promenade, and city parks starting Saturday, the city said. Social distancing remains required during all outdoor recreation.

New Jersey reported 311 new deaths on Friday, increasing the state’s death toll to 7,538, the second highest in the country. The number of positive COVID-19 cases rose by 2,651, bringing the state’s reported total to 121,190. Hospitalizations were down 28% from an April 14 peak, with 5,972 patients checked in.

And in Delaware, where Republican lawmakers called on the governor to begin reopening the economy, Gov. John Carney said the infection’s trend lines were heading in a positive direction but the state is not yet ready to begin loosening restrictions.

Pennsylvania leads the way in the region with its phased experiment.

“Over the past two months, Pennsylvanians in every corner of our commonwealth have acted collectively to stop the spread of COVID-19,” the governor said. “Each of these actions seems small individually, but taken together, they built a very powerful weapon against COVID-19.”

The yellow phase still carries many restrictions. Residents must continue social distancing and, unless impossible, telecommuting. Large social gatherings will be banned and many of the activities of daily life, from working to shopping to socializing, will still be curtailed. And should there be an uptick in cases, the governor said he would move swiftly to reinstate the strict closure and stay-at-home orders.

Gyms, theaters, indoor recreation centers, hair and nail salons, and schools will remain closed, and gatherings of more than 25 people will be prohibited. Restaurants and bars will continue to be permitted to remain open for takeout only. Casinos will also remain shuttered.

Companies will have to continue providing teleworking options to employees if their work can be done remotely. If they don’t have that ability, they will be able to reopen with certain safety precautions, which will be announced next week.

Child care operations can resume — also under guidelines that will be announced next week — and retail stores can reopen to customers, though curbside pickup and delivery remains preferable and certain safety precautions must be taken.

The counties will be able to move to the “green" phase, where most restrictions are lifted, if they do not experience outbreaks of the virus in the yellow phase.

To guide its decisions, the state is using a tool created with Carnegie Mellon University that looks at risk factors such as case numbers per capita, population density, hospital bed capacity, and the number of workers employed in a currently closed industry. Those metrics are then considered along with a county or region’s ability to conduct testing and contact tracing.

Though the administration said it would announce specific metrics for diagnosing and tracing cases, the plans released Friday left unanswered questions about how the state planned to increase testing and how many people were needed to complete contact tracing work.

Health care workers, academic institutions, volunteers, and possibly newly hired employees will work with the state Health Department to do contact tracing, which involves identifying anyone a sick person may have infected and telling them to self-quarantine.

The state plans “to hire people when needed” to do contact tracing and will use improved technology and workflow processes, Health Secretary Rachel Levine said.

Testing will still be focused on people with symptoms as well as high-risk populations, health-care workers, and first responders. Under Friday’s plan, the state’s population is broken down into six regions with a goal to test 2% of people in each of those areas monthly.

“We want anyone who has symptoms of COVID-19 to get tested,” Levine said, “and we’re trying to make that accessible and much easier" to do.

Staff writers Laura McCrystal, Erin McCarthy, Oona Goodin-Smith, and Rob Tornoe contributed to this article.