A four-year debate over the safety of the digital “smart meters” that Central Maine Power Co. has installed at almost every home and business it serves remained unsettled Tuesday at the Maine Public Utilities Commission after the two commissioners who will decide the case expressed different views on details of the matter.

Following deliberations, Commissioners David Littell and Mark Vannoy agreed that the radio-frequency emissions from the meters and their wireless networks don’t pose a health threat. But they differed on several details, including whether people who don’t want the meters at their homes can opt out for free after documenting health concerns through a doctor.

After roughly 90 minutes of discussion, the two men said they would write their legal opinions, which together will form the final order, or formal decision. That order is expected within two weeks.

But the uncertainty left questions about the options for customers who oppose the meters and blame them for medical and health problems, and activists who challenged the meters at the PUC and in court.

“Until the order comes out, I really can’t answer that question,” said Harry Lanphear, a spokesman for the agency.

Bruce McGlauflin, the attorney for activists who brought the case to the PUC, speculated afterwards that a medical opt-out could be the only way for the two commissioners to ensure that the meters meet safety requirements under PUC rules.

“Because there were such stark differences between the statements and analyses presented by Commissioners Littell and Vannoy, it is difficult to say whether there is enough agreement to issue one order,” McGlauflin said.

The commission’s chairman, Tom Welch, has recused himself from the case due to legal work he did for CMP when he was in private law practice.

In 2009, the PUC approved CMP’s plan to replace old-style analog electricity meters with digital smart meters for its 620,000 customers. Health activists soon objected, joined by residents who claimed that they suffered from various medical symptoms after the meters were installed. They appealed the PUC’s approval in court, arguing that the commission hadn’t met its legal obligation to ensure that the $200 million smart-meter program is safe.

In 2012, the Maine Supreme Judicial Court agreed with the activists and ordered the PUC to take a second look at the health issues.

The PUC doesn’t have the expertise to conduct its own health studies so it has relied on accumulated knowledge. It accepted thousands of pages of new testimony from experts across the globe. The case encompassed more than 660 separate filings, with reams of written and oral testimony from expert witnesses on the connection between brain tumors and the use of cellphones, for instance, and from residents who link the meters with symptoms that include headaches and fatigue.

After reviewing the testimony, the PUC staff wasn’t convinced that the meters pose a health hazard.

It said that the scientific evidence presented in the case is inconclusive. It found no credible, peer-reviewed studies to show a direct health risk from smart meters. The studies that do show a risk are based on exposures to much higher radio-frequency levels, the staff noted.

The staff also determined that the radio-frequency emissions from the smart-meter network comply with federal safety standards, and that no state or federal regulatory body or health agency in the United States or Canada has found smart meters to be unsafe.

During Tuesday’s deliberations, Littell said he was convinced that there was “some credible evidence” involving heath impacts from radio-frequency emissions, but that didn’t necessarily translate into the meters being unsafe. He noted, for instance, that much of the research dealt with cellphones, which are held up to faces, not electric meters mounted outside on walls.

“The amount of exposure matters,” he said.

But Littell said he was sympathetic to the 8,000 or so customers who have chosen to opt out of the smart meter program. While stressing that he can’t make clinical determinations, he said he understood that people who attribute medical symptoms to the meters find them real and debilitating. He recommended allowing people to have smart meters with their transmitters turned off at no charge, if a licensed medical doctor determined that they should avoid exposure.

Currently, customers who choose to keep their analog meters have to pay a one-time charge of $40 and a recurring monthly charge of $12. For customers who choose the transmitter-off option with the new meters, there is a one-time charge of $20 and a recurring monthly charge of $10.50.

Vannoy said he couldn’t go along with the free opt-out. He said the overall finding of the PUC staff is that the meters pose no credible safety threat to human health. People who opt out of having them installed, or having the wireless transmitters turned on, should pay for the added costs of the alternative system, he said. Vannoy noted that when some customers don’t pay for a service, other customers absorb the costs.