The contingency plans, he said, provide the new president a variety of possible responses to certain situations rather than a specific course of action. “It’s a menu of contingencies and potential options,” he said. “It’s not exhaustive, and it’s not exclusive, and it’s not prescriptive, as if to say, ‘These are the only things you can do.’ ”

Mr. Bush said Tuesday that a top priority in his final days in office is to help Mr. Obama get ready to govern. “We care about him,” he said in an interview with CNN. “We want him to be successful, and we want the transition to work.”

A spokeswoman for Mr. Obama’s office said she had no comment. But other Democrats working with the transition said they appreciated the Bush team’s efforts. “This doesn’t absolve the Bush administration of some of their judgments they’ve made over the years, but this is the right thing to do,” said a Democrat close to the transition who did not want to be named to avoid alienating the team. “This is when enlightened self-interest works.”

Mr. Cressey, who has been a critic of Mr. Bush’s national security policy, said: “I give them a lot of points for doing this. There could be zero down time for the new team coming in.”

The attention to national security in this postelection interim period stems in part from the recognition that terrorists have struck during moments of flux in national leadership before. Al Qaeda’s first attack on the World Trade Center in 1993 came weeks after Mr. Clinton was sworn in. A series of bombings on a Madrid commuter train system in 2004 came three days before national elections. And an attack on a Glasgow airport in 2007 came days after Prime Minister Gordon Brown took office in Britain.

Here in the United States, the Department of Homeland Security declared the fall election and transition a period of heightened alert because of the concern. Under the authority granted by intelligence legislation Mr. Bush signed in 2004, the government has processed security clearances for Obama transition officials earlier than ever before and Mr. Obama has named his top nominees faster than any other modern president-elect.

Beyond terrorism, Mr. Obama could face an early unexpected international test on any number of fronts, as his running mate, Joseph R. Biden Jr., predicted on the campaign trail. During the transition between the administrations of the first President Bush and Mr. Clinton, a humanitarian crisis in Somalia prompted Mr. Bush to send United States troops to intervene.