When it comes to environmental issues, the Bush administration seems determined to destroy its own limited credibility.

The latest example involves the administration's proposal to deal with mercury emissions from power plants. Earlier this week, a bipartisan group of senators, a former head of the Environmental Protection Agency, and health, labor and religious groups, all urged the Bush administration to withdraw its controversial proposal to create a trading system for mercury emissions (e.g., letting utilities that exceed standards sell "allowances" to those that don't) without Congressional authorization. The same day, the Los Angeles Times quoted several unnamed career EPA officials who alleged the agency was pressured by the White House to refrain from fully scrutinizing the potential health effects of its mercury proposals.

As long-time advocates for the use of market forces like emissions trading to support mandatory limits on dangerous pollutants, we would add to the growing list of the Bush administration's environmental sins its ability to misapply and undermine even good ideas.

In this case, the pattern of administration malfeasance is clear. The best way to deal with power plant pollutants is to cap them all, and then allow emissions trading under closely regulated conditions. But the Big Bertha of power plant pollutants is carbon dioxide. Like mercury, it is produced when power plants burn coal to generate electricity. Control carbon, and many mercury emissions can be prevented from happening in the first place through the cleaner technologies that utilities and other sources of pollution would quickly begin to adopt.

In its first and most famous "flip" on environmental issues, the Bush administration abandoned a campaign promise to support a cap-and-trade system for carbon dioxide, sulfur dioxide, nitrogen oxides, and mercury. But its pursuit of a similar system for mercury alone not only ignores avenues for preventing mercury emissions through a broader system of market-based controls, but also ignores the key difference between mercury and greenhouse gases: It's dangerous to human and animal life here on earth, whereas gases such as carbon dioxide are only problematic in the earth's upper atmosphere, where they trap sunlight and gradually warm the planet.

An isolated cap-and-trade system for mercury, as the Bush administration is proposing, unless strictly regulated, could allow major mercury emitters, especially coal-fired utilities, to create mercury "hot spots" threatening the health and safety of nearby communities -- and ultimately the economy and the quality of life.

To sum it up: Imposing a cap-and-trade system for mercury without a similar system for carbon dioxide and other emissions is a bad idea. Doing so by the back door of EPA regulation rather than a full debate in Congress is an even worse idea. And entrusting mercury regulation to an administration characterized by chronic disrespect for scientific evidence, close alignment with the Flat Earth wing of conservative activists, and all-too-cozy relationships with special interests, is a truly terrible idea.