A federal appeals court refused Thursday to make a resistant Bush administration speed up a decision on whether greenhouse gases and global warming threaten public health and welfare.

The U.S. Court of Appeals for the District of Columbia denied a petition by 17 states and several environmental groups asking it to order the Environmental Protection Agency to make that determination within 60 days.

Such a finding is a necessary first step to regulating carbon dioxide and other greenhouse gases from motor vehicle tailpipes and the smokestacks of refineries, power plants and factories. The Supreme Court more than a year ago ruled that the EPA has the authority to regulate greenhouse gases under the Clean Air Act, a step President Bush has repeatedly refused to take.

Instead, EPA is expected to issue a proposal in coming weeks that seeks public comment on a range of options the agency could take to control greenhouse gases under current law.