Just when you thought it was safe to go home and hide under the bed from all the bad news about the environment, the government warns that a man's house may be a menace because of cancer-causing radon gas. No wonder the mood of the moment is ecophobia, the fear that the planet is increasingly inhospitable.

If you go to the beach to brood about this, do not sit in the sun. The thinning ozone layer raises the risk of skin cancer. And do not go near the water which, even if it is free of medical waste, may have other pollutants that degrade it even more than acid rain is degrading lakes.Any widespread anxiety should have a political echo, and ecophobia should serve the Dukakis campaign.

It may do for Michael Dukakis what his attempt to portray today's prosperity as a chimera can not do. It gives him more than a subject; it gives him a theme - stewardship. He can ask: Has growth been purchased at too high a price? The price can be measured in accumulated public debt and the inadequate husbandry of the Earth's resources.

George Bush says, "I am an environmentalist." That statement is as vacuous as any statement that can be constructed from four English words. Does Bush's environmentalism dicate a "let burn" policy regarding forest fires? Is he for higher fuel-efficiency standards for automobiles, standards that would mean smaller cars and higher fatality rates?

Dukakis is no different. He will not challenge any popular behavior, regardless of its environmental impact. Instead, there will be tough talk about easy choices, such as "cracking down on polluters" - as though the environmental danger comes down to a few bad people putting things where they do not belong.

Draw a deep breath and consider this. In 1900, America's cities contained three million horses, the healthiest of them producing up to 25 pounds of manure a day. Manure in the streets attracted swarms of flies until, in hot weather, traffic ground it into a dust that (a memoirist wrote) "flew from the pavement as a sharp, piercing powder, to cover our clothes, ruin our furniture and blow up into our nostrils." Then came a solution - one of today's problems, the internal combustion engine.

Want a new worry? Space junk. Science magazine says there are 48,000 man-made objects one centimeter or larger orbiting Earth.

Man is messy, but any creature that can create space vehicles can probably cope. That is, mankind's inventiveness has been, so far, more creative than mankind's environmental impact has been damaging. So far. What is still missing is the political ingredient, a sustained summons to stewardship.