(CNN) President Donald Trump told US governors on Thursday his administration was preparing to issue new, potentially more relaxed social distancing guidelines based on geographic risk factors for the novel coronavirus, even as some health experts warn it's too early to allow Americans to congregate in large groups or return to their workplaces.

In a letter, Trump said new coronavirus testing capabilities would allow his administration to identify "high-risk, medium risk and low-risk" counties where different levels of social distancing would be appropriate.

"Our expanded testing capabilities will quickly enable us to publish criteria, developed in close coordination with the Nation's public health officials and scientists, to help classify counties with respect to continued risks posed by the virus," he wrote.

New, more tailored guidelines will help governors and other state policymakers decide on "maintaining, increasing or relaxing social distancing and other mitigation measures they have put in place," Trump wrote.

Not all members of the White House coronavirus task force had seen Trump's letter before it was released publicly, a task force source said, who added the President's plan detailed in the letter is still a work in progress.

The President has been itching to loosen the 15-day social distancing measures he announced last week in a bid to prevent the spread of the coronavirus.

During an early evening news conference, Trump repeatedly stressed the US "has to go back to work" but suggested social distancing guidelines could be used as they returned.

"When we are open, as soon as we open, that doesn't mean you will be stop the guidelines. You will still try and distance yourself. Maybe not to the same extent because you have to lead a life, but the timing is coming," Trump said.

Even as he's agitated to relax the guidelines, however, some state governors have implemented new restrictions on nonessential businesses and large gatherings.

Trump said this week that he'd like to see the country "raring to go" by Easter, on April 12, a date that many health experts say is unlikely.

"There is still a long battle ahead, but our efforts are already paying dividends," he wrote in the letter. "As we enhance protections against the virus, Americans across the country are hoping the day will soon arrive when they can resume their normal economic, social and religious lives."

Some of Trump's health advisers have warned that loosening guidelines on social distancing before the virus is contained would worsen its spread. They have cautioned against creating arbitrary deadlines on reopening the country.

"You've got to understand that you don't make the timeline, the virus makes the timeline," Dr. Anthony Fauci, the nation's top infectious disease specialist, said on CNN on Wednesday. "So you've got to respond in what you see happen. And if you keep seeing this acceleration, it doesn't matter what you say. One week, two weeks, three weeks -- you've got to go with what the situation on the ground is."

Trump has insisted that as conditions improve in certain areas of the country, or don't devolve into large outbreaks, that business should be able to return to normal.

But he's also said that widespread testing isn't necessary in those areas because they don't have large caseloads.

"We could go to certain states right now that have virtually no problem or a very small problem. We don't have to test the entire state in the middle west, or wherever they may be. We don't have to test the entire state. I think it's ridiculous. We don't have to do it," he said during a briefing at the White House on Wednesday. "A lot of those states could go back right now, and they probably will because at some point in the not-too-distant future, certain states are going to come off the rolls."

Ahead of the letter's release, Trump discussed the potential new distancing guidelines with governors during a phone call, according to a person familiar with the call.

On the call, Trump reiterated his view that the country needs to reopen soon and that not every place needs to be under the same restrictions. He said certain places had almost no problems with the virus and shouldn't be kept to the same restrictions as areas with high case loads.

Some governors on the call thanked Trump for moving away from a nationwide guidance, saying it didn't work for their states.

But others were less enthusiastic. Trump and Washington State Gov. Jay Inslee got into a heated discussion over Trump's unwillingness to use the Defense Production Act to secure more equipment for states.

Inslee told Trump he needed to act as the "Tom Brady" of the response effort after Trump said the federal government would act as the "backup" for states' own efforts. Trump said the federal government had already done plenty for Washington State.

Other governors weren't as combative but did raise some issues with how the federal government has handled the situation, including access to tests.

CNN's Jim Acosta contributed to this report.