It's a handsome house, an almost-new colonial in a woodsy Rockport neighborhood. John Bragg, a broker at deRochemont Realtors in Rockland, was happy to have the $475,000 listing under contract in January.

But then something unexpected happened. A routine air test by the buyers found elevated concentrations of radon, just as Bragg was learning that the state had lowered its recommended action level for dealing with the cancer-causing gas.

When the buyers heard about the new guidelines, they backed out of the sale. Their concern, Bragg said, was that radon-removal equipment might not be able to achieve the new goal.

Now the house is back on the market. And Bragg is left wondering why he didn't know about the new guidelines, so he could explain them to the seller and buyers. Maybe he could have kept the deal on track.

''It was just kind of dropped on us,'' he said. ''We were caught off guard.''

Bragg's complaint isn't uncommon this winter, according to the Maine Association of Realtors. Brokers already are coping with a slow housing market. Now they're calling the trade group about losing sales to radon confusion. They're unclear about what the revised guidelines mean and whether government rules will make some homes impossible to sell.

For its part, the state is trying to clarify the new radon recommendations for Realtors and address concerns about the impact on business.

Behind these exchanges is an evolving policy to elevate radon to a major public health issue in Maine.

Here's why: Radon is considered the second leading cause of lung cancer, behind smoking. Recent national studies have tied exposure in homes directly to the disease.

Maine soil and rock can contain high levels of radon, so every homeowner should test for radon in the air, state experts say. Any home on a private well should be tested for radon in the water, which poses a hazard when radon is vaporized into the air from showers and dishwashing.

That's not happening. The state estimates that only one in five homes are ever checked for radon. The risk typically is ignored until a house is being sold and buyers ask for a test as part of the home inspection process.

That's why the impact of the new guidelines is being felt immediately in the housing market. And with government experts guessing that half the homes in Maine may have radon levels above the new threshold, more home sellers and their brokers could be in for surprises in the months ahead.

Radon testing has been common in Maine for more than 20 years. It's not illegal to sell a house with high radon levels, but brokers and sellers are required to disclose the information. Only state-registered testers can test a house that's for sale; only state-registered contractors can install treatment systems in these cases.

TIGHTENED GUIDELINES

The basis for all this activity is what health experts call a maximum exposure guideline. It represents levels of chemicals in air and water, below which there's minimal risk of disease.

Until this year, the Maine Center for Disease Control & Prevention set the guideline for radon in water at 20,000 picocuries per liter. Above that, homeowners were encouraged to consider a treatment system. While the federal government focuses its guidelines more on air than water, some states have significantly lowered the water limit - New Hampshire is at 2,000 pCi/L. So Maine decided that 4,000 pCi/L was a prudent compromise.

''This change was long overdue,'' said Andrew Smith, the state toxicologist.

Lowering the water limit also led to a review of the guideline for airborne radon, Smith said. The federal Environmental Protection Agency has been recommending that homeowners consider taking action with an air radon reading between 2 and 4 pCi/L. But in Maine, Smith said, many brokers and some treatment system contractors have focused exclusively on the 4 pCi/L figure.

''Realtors are acting like 4 pCi/L is a bright line and below that, you're safe,'' Smith said.

The new health studies, he said, make it clear that air radon levels above 2 pCi/L present a public health concern. So after surveying treatment contractors late last year, state officials decided to tighten up the air and water guidelines.

Problem was, they didn't get the word out to brokers, who are on the front lines of radon testing. Brokers started hearing about the change from building inspectors performing pre-sale checkups, and then from upset homeowners.

''They have a valid criticism,'' Smith said. ''I think we could have given them more of a heads-up.''

In late January, Smith started hearing from Linda Gifford, a lawyer who represents the Realtors association. Among her concerns was the science behind the new guidelines and indications that treatment contractors couldn't always meet the 2 pCi/L air level, or could do so only at great expense.

''What do we do about all these newly stigmatized properties?'' Gifford asked Smith in an e-mail. ''You say 'guideline' and remarkably, folks still think the government knows best in all matters and hear 'law.' And in a market where there are lots of properties available, it may mean some become unsaleable.''

SORTING OUT IMPACT

The Rockport colonial John Bragg is trying to sell certainly doesn't fall into that category, but the owner had to pay $1,500 for a treatment system that removes radon from the air beneath the basement floor. The system has cut radon levels from more than 8 pCi/L to half a picocurie/liter, well below the threshold. Too late, though, for the buyers who were scared off by the confusion.

''The buyer just decided not to pursue the contract,'' Bragg said.

This scenario is familiar to Eric Wilson, sales manager at Air & Water Quality Inc. in Freeport. His company installed the air treatment system in Rockport. He's getting plenty of calls from brokers, buyers and sellers who are confused about the new guidelines.

''Everybody's in a panic, trying to figure out what to do,'' he said.

He tells callers that systems costing roughly $4,000 can knock down water radon levels to 4,000 pCi/L. The technology is good enough that he can offer a written guarantee on water.

Air levels are a different story. On newer homes with concrete basements underlaid with crushed stone - like the one in Rockport - Wilson can install venting systems for $1,500 or so that hit the 2 pCi/L target. But it's more challenging in an old farmhouse with a dirt cellar, for instance, or a home built on more than one concrete slab. Air & Water Quality won't offer a guarantee in some of these cases, because the technology is imperfect and the testing margin of error at 2 pCi/L is high.

''From a business viewpoint, it's a huge liability,'' he said.

As the spring home-selling season approaches, Realtors and health officials are talking about ways to increase public awareness of the new radon guidelines. They hope home-owners will start testing their homes now, both to cut the risk of radon exposure and of scuttling a future real estate deal.

''This is an opportunity to get people thinking about radon,'' Smith said.

Staff writer Tux Turkel can be contacted at 791-6462 or: tturkel@pressherald.com