WASHINGTON  With just 15 days left in office, President Bush announced Monday that he had ordered an immediate airlift to deliver vehicles and equipment to the war-torn Darfur region of Sudan to bolster a struggling international peacekeeping effort there.

Mr. Bush waived a requirement that he notify Congress 15 days before undertaking such a mission, because waiting would “pose a substantial risk to human health and welfare,” the White House national security adviser, Stephen J. Hadley, said in a statement.

The White House said the airlift had been in the planning stages for months. But some human rights activists expressed puzzlement at the timing of the move, a little more than two weeks before the inauguration of Barack Obama. Mr. Obama has vowed more aggressive action in Darfur, including imposition of a no-flight zone, a move Mr. Bush has declined to make.

“It is certainly more than passing strange to have the national security adviser come out and say that this step is being taken and Congressional notification is being waived because of the urgency of the situation in the last two weeks of the administration, when Darfur has been on fire for five years,” said John Norris, executive director of the Enough Project, a group here that campaigns against genocide.