Is your cell phone hazardous to your health? The short answer is "not as far as science has determined."

Experts say there is no conclusive evidence that the low levels of radiation cell phones emit pose a health risk. And with about 87 percent of Americans using cell phones and 4 billion mobile phone users across the globe, that’s good news.

But one environmental advocacy group cautions that until more long-range studies are conducted, people should consider cell phone radiation and take precautions against prolonged exposure.

The Environmental Working Group recently released a report that ranks cell phones by the watts per kilogram of radiation they put out. Last week, lawmakers in Washington, D.C., heard from scientists about the long-debated link between cell phone radiation and some forms of cancer.

To be sure, the Federal Communications Commission, Food and Drug Administration, American Cancer Society and the National Cancer Institute all say there is no proven health risk posed by cell phones. In 2003, an extensive FDA study concluded that "the weight of scientific evidence has not linked cell phones with any health problems."

The Environmental Working Group, however, cautions that the FDA and other agencies relied on short-term studies that looked at risks over a three-year span.

"It is not conclusive," said Nneka Leiba, a researcher for the Washington, D.C.-based nonprofit group. "We think further research needs to be done. And until it is conclusive, we feel like people should use a precautionary principal."

The group’s radiation rankings have five Samsung models among its six "best" phones for low-level radiation, along with Motorola RAZR V8. All put out less than 0.50 watts per kilogram of radiation.

Among the phones with the highest radiation output, the T-Mobile myTouch 3G and Motorola MOTO VU204 both have 1.55 Watts per kilogram, just under the FCC’s limit of 1.6 watts per kilogram.

"There’s a wide range on the market," Leiba said, adding that there was "no one brand or type" of phone that puts out more radiation than others.

By law, cell phone manufacturers must list the wattage of the phone somewhere inside the packaging, and consumers can look it up on a FCC Web site by consulting an FCC identification sticker located underneath the battery of the phone.

The Environmental Working Group wants manufacturers to display the radiation values on the box, "so that people can know what it is before they buy a phone," Leiba said. "Right now you have to buy the phone first."

The Cellular Telephone Industry Association said it relies on the views of impartial health organizations.

"The peer-reviewed scientific evidence has overwhelmingly indicated that wireless devices do not pose a public health risk," said John Walls, the CTIA’s vice president for public affairs.

The Environmental Working Group also wants the FCC to revise its radiation wattage standards, which were put in place in 1992, when far fewer children were using cell phones. Some scientists believe children are at greater risk than adults from low-level radiation.

Today, about 70 percent of children 12 to 17 use cell phones daily, according to the Pew Internet and American Life Project.

The Environmental Working Group said basic precautions like using hands-free headsets and texting more than talking are already being used.

"We don’t want to put a doomsday attitude out there, because we’re still using our cell phones," Leiba said. "But we want people to be aware that new science is out there, and it is raising some issues. And with consumer awareness will come more studies."