A few years back, Utah had a problem with radioactive radon gas collecting in some buildings. The invisible, odorless gas is a major contributor to lung cancer. It was a man-made problem, the result of using tailings from a uranium mill as fill under foundations.

But many other parts of the country are discovering they have radon gas problems of their own - not as a result of anything man has done, but simply from the workings of nature.Radon gas is released in minute quantities due to the decay of trace amounts of uranium found in all rocks and soil. The gas tends to enter buildings through cracks in foundations and other openings. It gets trapped in homes and is inhaled into lungs where it leaves its own radioactive decay products.

What's the danger? The National Academy of Sciences estimates that 13,000 people die each year from radon-caused lung cancer - about 10 percent of all lung cancer deaths. EPA officials said this is 10 times worse than the hazard from outdoor air pollution.

The news is even worse for smokers who already are putting their lungs at risk. Smoking makes radon 15 times more effective in doing damage to the lungs.

The EPA has set 4 picocuries of radon per liter as its "action level." Yet 4 picocuries of radon has not been determined as harmless, either. Radon measured outdoors amounts to about one-half of 1 percent of that amount. Indoors, it builds up to heavier concentrations, particularly in today's well-insulated homes.

A survey of 10 states last year by the Environmental Protection Agency indicated that perhaps one in 10 American homes had a radon problem. But a study of 10 more states released this week showed more widespread and higher levels of radon than earlier believed.

The latest survey found 63 percent of the homes in North Dakota above the 4 picocurie level. Minnesota, 46 percent; Pennsylvania, 37 percent; Indiana, 26 percent; Massachusetts, 24 percent; Missouri, 18 percent.

So what's to be done?

The first advice is: don't panic. This is not a sudden, new problem. What's true in one state, may be entirely different in another. There is no indication that radon is a critical issue in Utah. No EPA study has been done here, but Wyoming and Arizona have not shown major radon levels.

Initial screening tests for radon can be done for $10 to $25. If they show a high amount, a followup test can be done. Fixing a house to seal it against radon can be expensive, depending on what is needed. Perhaps $1,000 would be average, but that's an uncertain figure.

A word of warning. Unscrupulous scam artists may try to frighten people into having expensive tests and even more expensive repairs. Stay calm and don't fall for pitches based on scare tactics. The safest bet is to say "no" to such approaches.

The EPA has authorized some 1,000 companies to do radon testing. The names of such companies may be obtained by writing EPA's regional headquarters in Denver, 999-18th St., Denver, Colo. 80202.

One thing is clear. A safe and healthy environment doesn't come easy. Even living in a house has its drawbacks.