National Academy of Sciences report reaffirming the threat of global warming, and declaring fearlessly that human activity is largely responsible for it, virtually requires President Bush to engage an issue he has consistently underestimated. It also provides another compelling reason for his administration to rewrite an unbalanced energy strategy that relies far too heavily on producing more of the same fossil fuels that lie at the root of the warming problem.

Mr. Bush began his tenure by abandoning a campaign pledge to seek national limits on carbon dioxide, the main global warming gas, and by renouncing the Kyoto Protocol, the 1997 treaty that committed industrialized countries to mandatory reductions of carbon dioxide and five other greenhouse gases. Ever since, and well before the academy's new report, pressures have been building on Mr. Bush to reverse course. Japan and the Europeans have been urging him to rethink his rejection of Kyoto, and Congress is considering legislation that would require significant reductions in carbon dioxide emissions.

Meanwhile many of Mr. Bush's natural allies in the corporate community, ignoring his indifference to global warming, have taken unilateral steps to control emissions of greenhouse gases, partly for environmental reasons and partly because the efficiencies required to achieve such reductions make sound business sense. DuPont is aiming to cut its emissions by 40 percent, and Alcoa, which until recently was run by Mr. Bush's Treasury secretary, Paul O'Neill, plans reductions of 25 percent. These are huge reductions. Even foreign companies are signing up. Just this week Pemex, the Mexican oil giant, agreed to a 10-year program of carbon dioxide reductions that was devised in conjunction with Environmental Defense, an American advocacy group.

Mr. Bush should be leading this parade, not watching it. To be sure, there have been cabinet-level discussions in recent days aimed at devising proposals he can take with him on his European visit next Tuesday.

Environmentalists who were largely ignored during the creation of the administration's energy plan have now been drawn into discussions about possible improvements to it. And yesterday, confronted with a report that Mr. Bush himself had ordered up, the White House grudgingly and belatedly acknowledged the existence of "sound science" on which to base a global-warming policy. But the administration gave no indication of what that policy might be, nor was there any suggestion that it is ready to undergo two fundamental changes in attitude and policy essential to any sensible strategy.

The first would involve a profound rethinking of the administration's energy proposals, now heavily weighted toward increasing energy supplies, particularly fossil fuels. A more balanced and indeed less costly approach would embrace an aggressive program of energy efficiency aimed at producing more fuel-efficient cars and moderating demand for electric power.

The second and perhaps more important step is for Mr. Bush to accept the fact that there can be no solution without American leadership. The United States must lead not only because it is the world's biggest offender, producing one-fourth of the world's greenhouse emissions with only 5 percent of the population, but because for all of Mr. Bush's diffidence on the issue, it is still the country to which other nations turn first for policy guidance and technological inspiration.