SOME OF President Obama’s unilateral actions may raise legitimate concerns, even for those who believe this Congress is noxiously unproductive. But his demand that cars and trucks use less fuel raises no such question. The president’s plan rests on a ­rock-solid legal foundation. It’s also the right thing to do while lawmakers dither on climate change.

Last week Mr. Obama said his administration would use the powers it has under various laws to press for tougher efficiency standards for heavy trucks. A relatively small number of these massive vehicles produce about a quarter of the transportation sector’s greenhouse gas emissions, according to the White House. That doesn’t mean truckers are particular climate villains; the country depends on them to bring 70 percent of the nation’s freight tonnage to market, and big trailers use a lot of fuel. But if they can reduce fuel consumption and emissions at little or no cost, they should.

That’s where the Obama administration is stepping in. Many truck upgrades will pay for themselves over time in saved fuel. But truckers might be discouraged by the upfront investments required. Truck manufacturers might be reluctant to invest in fuel-saving technology without assurance that the market will recognize its value. Neither group has to account for the environmental costs of excessive fuel use, absent government intervention of some kind. So the government has set standards that require efficiency improvements across the country’s heavy-truck fleet, and the president wants those standards toughened, with final rules coming next March.

As the Obama administration hashes out its regulations, flexibility will be needed. The government should set reasonable top-line efficiency goals without meddling in how manufacturers meet the mandates, whether by using new engine lubricants, producing better tires or making tractors and trailers more aerodynamic. That approach might not satisfy the electric-car or alternative-fuel lobbies, but it would result in efficiency upgrades at minimum cost. On the other hand, special tax credits for alternative-fuel vehicles and infrastructure, which the president also supports, waste taxpayer money.

In fact, the best approach to global warming would be for the government to tax carbon dioxide emissions commensurate with their harm and then get out of the way. That would be more efficient than setting fuel efficiency standards; it would wring carbon out of the whole economy, not simply out of the transportation sector, starting with where it is cheapest to do so. But Congress would have to approve such a plan, and lawmakers remain determined to resist the obvious on climate policy.

Until that changes, the president is right to use the anti-emissions weapons the law offers him, carefully but with determination.