But industry groups did what industry groups often do when faced with unpleasant regulations: They sued. The agency had overstepped its authority, they claimed, and abused its congressional mandate under the Clean Air Act.

On Wednesday, the U.S. Supreme Court will hear oral arguments in two linked cases involving the new emissions standards -- just one day after the election that will determine who gets to appoint any new justices for the next four years. And much more than the power of a single agency is at stake: The EPA cases represent one of the greatest challenges to federal regulation in years. Most Americans don't think of the Supreme Court as an arbiter of public health, but how the closely divided court rules on this issue could have monumental impact on how much latitude all federal agencies have to safeguard the public welfare.

In the presidential campaign, much of the discussion over possible Supreme Court appointments has focused on the fragility of Roe vs. Wade, the landmark 1973 ruling that legalized abortion. As critical as preserving Roe is, the EPA cases make clear that the next president could play a vital role, through his eventual nominees, in the ongoing struggle between conservatives who want to curb federal power and liberals who do not.

The court gave some indication of its leanings in a case earlier this year when it ruled that the Food and Drug Administration does not have the authority to regulate tobacco. That 5-4 decision -- with Anthony Kennedy and Sandra Day O'Connor joining conservative stalwarts William Rehnquist, Antonin Scalia and Clarence Thomas -- must have given Joe Camel reason to smirk.

After being pummeled by anti-smoking forces for years, the tobacco industry reveled in its rare victory. By rebuffing President Clinton and throwing major roadblocks in front of the government's anti-smoking initiative, the court's ruling will have a profoundly negative impact on public health because it blocks federal efforts to protect the nation's youth from the hazards of smoking. A broad array of FDA regulations to discourage teenage smoking -- from advertising restrictions to rules governing sales to minors -- are threatened in the wake of the court's decision.

In the issue before the court, the EPA regulations seek to tighten emissions standards for ozone, a key component of smog, and particulates, tiny bits of matter that are a byproduct of fuel consumption. But many industry trade groups and conservative organizations with little interest in the environment, fearful about what they view as excessive regulation by Washington bureaucrats, have lined up to support the plaintiffs in Browner vs. American Trucking.

The case gained national attention when industry groups won a dramatic victory in federal appeals court last year. Now it is up to the nine justices to decide whether the EPA usurped Congress' legislative role in enacting the tough standards. They will also rule on whether the agency must weigh the cost of new regulations before establishing controls -- another issue that could have broad impact on how federal agencies do their jobs.