This may seem narrow and technical, but it’s actually extremely significant:

The White House has raised last-minute concerns over regulation of automobile emissions and fuel economy that aides said Tuesday could lead to a presidential veto of the energy bill now before Congress.

The bill, which passed the House and is pending in the Senate, requires automakers to meet a fleet average of 35 miles per gallon by 2020, but does not specify which government agency should enforce the new rule.

Primary regulation of mileage standards has historically fallen to the National Highway Traffic Safety Administration, an arm of the Transportation Department. But vehicle tailpipe emissions are regulated by the Environmental Protection Agency, and a Supreme Court ruling this year affirmed the E.P.A.’s authority to regulate emissions of the greenhouse gas carbon dioxide from passenger vehicles, which basically would mean regulating their fuel use.

The administration’s argument is that the energy bill will create unnecessary confusion over which agency has proper jurisdiction over mileage standards. And at a glance it seems like a reasonable argument. But, of course, it’s absolutely not reasonable at all.

This is better understood as a bank-shot effort by the Bush administration to block the EPA from functionally regulating carbon emissions from automobiles on behalf of the interest groups that don’t want to be bothered with reducing auto pollution.

Assuming the CAFE standard is signed into law, it will slowly ratchet up fleet efficiency standards until they top off at 35 miles per gallon. As a corollary, this will lower vehicle emissions, but as far as the Department of Transportation is concerned, that’s just a side effect. Their duty is to enforce the law as enshrined in the energy bill itself.

By contrast, the EPA, in the wake of a recent Supreme Court ruling, now enjoys a command and control authority that’s independent from the letter of the energy bill. If, hypothetically, a future president enacts a law that mandates specific, nationwide emissions reductions — and if meeting those reductions goals requires further decreasing vehicle emissions — then a responsible EPA administrator can effectively increase CAFE standards by mandating those decreases. The auto companies would have to respond.

All that is, of course, if the Democratic version of the CAFE standard is signed into law.

It’s an extremely important power and it may prove vitally necessary to the effectiveness of a future climate change bill. But that’s only if you actually care about the problem at hand and don’t see sheltering auto and oil interests as a greater priority for the country. Perhaps it’s no surprise, then, that President Bush has suddenly decided he wants this provision stripped from the energy bill as well.