The Environmental Protection Agency (EPA) has been working on an overhaul of the Clean Air Act's so-called New Source Review rules. The rules, which were strictly enforced by the Clinton administration, require electric power plants and oil refineries to install expensive pollution control equipment when they make significant modifications or repairs to the facilities.

The Bush plan, which has been the target of intense lobbying by environmental groups and electric utilities, is expected to be released this month, industry sources told Reuters.

Blumenthal would not comment on which other states might join such a lawsuit.

At a press event scheduled for Tuesday in Washington, nine state attorneys general will warn the Bush administration not to weaken the Clean Air Act. The event will be led by Eliot Spitzer, New York's outspoken attorney general.

Other states participating in Tuesday's event are Connecticut, Maine, Maryland, Massachusetts, New Hampshire, New Jersey, Rhode Island and Vermont.

Environmental and congressional sources say the administration's plan is expected to increase the amount of maintenance that companies can perform before triggering the rule.

Utilities say such requirements will allow them to maintain their plants to meet rising power demand without incurring expensive modification requirements.

A lawsuit would seek to compel the administration to keep the existing maintenance requirements "so as to preserve the intent of Congress," Blumenthal said. The objective "would be to stop a gutting of standards that are inconsistent with the Clean Air Act," he added.

The industry and the Bush administration claim the regulations prevent more refineries and power plants from being built or expanded, which in turn reduces available energy supplies.

Green groups see the White House efforts as a roll back of the 1970 Clean Air Act, fearing a package of loopholes to allow utilities to pollute more with fewer penalties.