Congress is taking steps to set standards for indoor radon levels that would be stricter than the current Environmental Protection Agency guideline, which critics charge is lulling homeowners into a false sense of safety.

But the effort is meeting resistance from EPA officials, real estate brokers and builders who say the measure could be a costly cure for the naturally occurring radioactive gas that can seep into homes and cause lung cancer.

The attempt to establish a national radon standard centers on legislation introduced by Rep. James J. Florio (D-N.J.) that is currently pending in the House subcommittee on health and the environment. It would require the EPA to set a standard based on health considerations, not cost considerations, which Florio acknowledged would most likely result in a level much more stringent than the agency's current radon guideline of 4 picocuries per liter of air. If a person is exposed to that level of radon for 18 hours a day for a year, it is the equivalent of undergoing 200 chest X-rays in a 12-month period. At that level, the agency recommends people take steps to reduce radon levels in homes.

Another proposal being discussed as an alternative to Florio's bill would not set a standard, but would force the EPA to do away with its current guideline. Instead, that measure would establish a goal, but not a standard, for indoor radon levels of 0.25 picocuries, or background levels, according to an aide to Rep. Henry A. Waxman (D-Calif.), the health and environment subcommittee chairman.

The measures appear to be gaining support in both the Senate and House. Although Florio's bill has yet to be circulated for cosponsors, the Waxman aide said Waxman may attach it to a popular piece of legislation to boost its chances. The legislation, which would give states $10 million to test schools for radon and develop other programs to combat the radioactive gas, has wide backing in the House.

The Senate already has passed a similar technical assistance bill, according to an aide to Sen. John Chafee (R-R.I.), a ranking Republican member on the environmental protection subcommittee. Chafee's aide said Florio's standards bill has support in the Senate and "would be looked at seriously."

The push for a national indoor radon level standard comes amid mounting concern over the EPA's safety standard and fears that it is lulling people whose homes test lower than 4 picocuries into a false sense of security. A National Academy of Sciences study released last month estimated that an average of two people per 100 will die from radon-induced lung cancer when exposed to 4 picocuries over a prolonged period, slightly more than the one person in 65 deaths the EPA had previously estimated. Local studies have shown that as many as one-third of all homes in the Washington area may have radon levels that exceed 4 picocuries.

"The EPA's 4 picocurie guideline serves as a de facto standard. It's not supposed to, but it's being regarded as such," Florio said. He noted that the risk the EPA tolerates for other carcinogens is much lower -- on the order of one in 100,000 deaths.

"I could accept one in 10,000 deaths {from radon}, but if we're talking about one in 65, that's something unacceptable," he said. But "right now everyone is saying just to bring {radon} levels down to 4 picocuries and under that amount not to do anything."

In contrast, Florio's legislation would require the EPA to set a standard based on the risk of contracting lung cancer from radon exposure and would not take into account the expense of meeting a specific standard. EPA officials said that the 4 picocurie guideline is based on what it would reasonably cost a person to reduce the danger in a house to that level, a figure they said is between $200 and $2,000.

Both Florio's bill and the compromise legislation that would set background levels as a goal are opposed by EPA officials. "As I understand it, Florio's approach is to set radon exposure at a safe level. And that's essentially setting it at zero," said Pat Quinn, director of the EPA's congressional liaison office.

"It is extremely problematic to try to achieve levels in a home below 2 picocuries. We can get there, but it is very difficult with the technology we have today," he said. Quinn acknowledged that the agency's guideline of 4 picocuries poses significant risks, "but you have to ask whether it is responsible policy to set those types of standards that Florio is talking about and not being able to put the tools in people's hands to mitigate those levels. A lot of the technology just isn't there. And all we'd be doing is scaring" homeowners.

He also said radon differs from other carcinogens the agency regulates more strictly because it occurs naturally. "We can't crack down on a polluter because there isn't any," Quinn said, pointing to difficulties enforcing a standard for a problem inside homes.

The attempt to set a radon standard also is encountering resistance from real estate brokers, who worry that a national standard would create problems in selling homes. David Weiss, director of energy, environment and development for the National Association of Realtors, said that "trying to hit a particular number is impractical when you can't even get a consistent measurement from day to day." He said that current testing methods are not reliable for the short-term readings that most people must use to determine whether they would buy a house.

Consequently, some sellers, whose houses would have to meet a standard possibly much stiffer than present guidelines, would be unable to sell their homes if a test produces an erroneously high reading, Weiss speculated. "It's just too early in our understanding of radon to set a national standard," he said.

Builders, too, have expressed reservations about a standard. Bion Howard, program manager for mechanical systems and energy for the National Association of Home Builders, suggested that the EPA's 4 picocurie guideline may be too tough. "There's considerable confusion over whether the EPA's guidelines are correct. In Canada, they have a 20 picocurie standard," he said.

Also, the costs of meeting a stricter standard may price some buyers out of the housing market. "Builders want to be able to build a safe house, but they still want to be able to sell it to someone," Howard said, claiming that techniques to meet a standard significantly below 4 picocuries would cost more and boost sale prices. Despite Howard's concerns, the NAHB has not decided whether to oppose a standards bill and their representatives will meet next month here to take an official stance.