MONTGOMERY, Ala. >> At a government laboratory in Alabama, workers in blue coats unload envelopes packed with small filters that trapped air particles in Hawaii, Alaska and elsewhere. The discs are placed in lead-lined, barrel-like devices for testing to make sure no traces of radioactive materials have wafted across the Pacific Ocean from Japan.

So far, the sea breeze in places like Honolulu is no more dangerous than the pollen-laden air of the Deep South, according to officials. Still, the 60 or so workers in the 72,000-square-foot building will be the first to know if the Japanese disaster spreads harmful amounts of radiation to the U.S. Minute amounts of radiation from Japan’s reactor have spread as far as the U.S. East Coast, though officials say it’s less harmful than the radiation people are exposed to on a routine basis.

Using super-sensitive equipment and computers linked to West Coast monitors by satellite connections that download new air-quality data each hour, experts hunched over monitors are scouring the atmosphere for any radioactive materials that could pose a threat to U.S. public health. There’s always some radiation in the environment — the testers are looking for abnormally high amounts.

Located on an annex of Maxwell Air Force base just a few miles from Alabama’s white-domed Capitol, the Environmental Protection Agency’s National Air and Radiation Environmental Laboratory has added a few extra contract workers because of the threat from Japan, officials say. And, as a precaution, it plans an early start to an annual program that tests milk for traces of radiation.

“I don’t expect to see anything, but we’ll have the data if we’re asked for it,” lab director Ronald G. Fraass said.

An electric plant with six nuclear reactors on Japan’s northeast shore was badly damaged by the earthquake and tsunami that struck March 11, prompting mass evacuations as the plant spewed radiation into the environment. Since then in Japan, radiation has been found in raw milk, seawater and 11 kinds of vegetables grown near the complex.

President Barack Obama, other leaders and scientists have tried to assure Americans that radiation from the Japanese disaster doesn’t pose a threat to the United States, but a hotline set up by health officials in California still was flooded with more than 1,000 calls about radiation.

And across the country, people have been ordering potassium iodide. The pills protect the thyroid from absorbing radioactive iodine, but they protect no other body parts nor against any other radioactive elements. Health officials have said there is no need to stock up on the pills.

The EPA’s monitoring system is aimed at providing another layer of assurance.

Long before the Japanese quake became a nuclear scare, EPA had a network of 124 monitoring stations scattered nationwide from California to Maine that were deployed mostly because of the threat of nuclear terrorism after the 9/11 terrorist attacks. The boxlike devices have bell-shaped inlets that constantly pull in air and test it for radiation. Data from those sites is sent by satellite links to the Alabama laboratory, where technicians monitor it constantly on computers for any unusual spikes.

After the earthquake, Fraass said, the agency added seven additional monitors in Hawaii, Alaska, Saipan and Guam as a first line of defense to detect any dangerous radiation moving across the Pacific Ocean. Expected to detect radiation amounts as little as a single hundredth of the government’s level of concern, the fixed monitors actually are detecting far smaller amounts, he said.

“Our system in the field is quite adequate to be able to see anything that would be of concern to the public,” Fraass said.

Aside from the digital monitoring, the detection devices are outfitted with circular white fiber filters that are bombarded with air pulled in from the environment. Those filters are removed twice weekly and sent by regular mail to the lab in Montgomery. The filters are small and the amount of radiation they contain poses no health risk to postal workers, Fraass said.

None of the tests run since the Japanese earthquake has detected dangerous amounts of radiation, he said. And the stepped-up monitoring is expected to continue until the last traces of radioactivity linked to the Japanese crisis are gone.

“Right now we’re only seeing a few that would trigger even a tenth of the level we normally count at, so in effect we’re not seeing anything that should be any concern for the American people,” Fraass said.