His holiday vacation was designed to be an island respite from the pressures of the White House.
Obama's military aide told the president about an incident aboard a plane as it was landing in Detroit just after 9 a.m. here. The president phoned his homeland security adviser and the chief of staff to the National Security Council for a briefing. Throughout the government, officials compared notes and reports about a Northwest Airlines passenger from Nigeria who, according to sources, claimed he was acting on orders from al-Qaida.
"We believe this was an attempted act of terrorism," one White House official said on the condition of anonymity to discuss the sensitive situation.
Later in the day, Obama made a surprise visit to military members to thank them for their service to the nation and meet with those in uniform executing his war plans.
Obama and first lady Michelle Obama made a quick trip to Marine Corps Base Hawaii after a private day exchanging gifts and eating a holiday meal of roast beef at their rented home in Kailua - between briefings on the disrupted plot of suspected terrorism. While the White House has said the president does not plan public events, the unannounced visit - accompanied only by a few reporters and his Secret Service detail - was an opportunity for the wartime president to meet with men and women of the military, some of whom have carried out his orders in Iraq and Afghanistan.
Wearing slacks and a casual shirt, the president made his way through the folding tables and booths and posed for pictures with the troops. They handed him cell phones so he could say hello to their parents.
Although the conversations were light - questions like "Where are you from originally?" - the commander in chief smiled broadly as he met with the troops, never giving a hint that he struggled for months with the question of whether to send more of them to Afghanistan.
"Thank you for your service," Obama said to many. Earlier in the day he visited the base to work out with his wife at its gym.
Obama visited the base last year as president-elect.
He has started the drawdown of U.S. troops in Iraq while dispatching thousands of more to an increasingly unpopular war in Afghanistan.
The Obamas dined on roast beef, potatoes and traditional fare at his $9 million rental home, White House spokesman Bill Burton told reporters traveling with the president. He said the first couple didn't exchange gifts with each other, although they did exchange gifts with first daughters, 11-year-old Malia, and 8-year-old Sasha at their rented estate on Oahu.
The Obamas planned their time as a low-key holiday away from the gridlock in Washington that has challenged the president's first year in the White House.
The vacation, the president's second since taking office, was delayed by a day while the Senate passed a version of his top domestic priority of health care. With versions of legislation passed in both the House and the Senate, Obama departed Washington on Thursday for a trip that was designed to keep the president out of the public view and give him a hard-earned break.
Officials emphasized that they did not plan to make news, as they did during the Obamas' summer vacation on Martha's Vineyard when they nominated Federal Reserve Chairman Ben Bernanke for a second term. During that week in Massachusetts, Obama's trip coincided with the death and funeral of Sen. Edward M. Kennedy, an Obama ally and legend.
On the latest vacation, the workspace for the traveling White House press corps included a camera-ready podium with U.S. flags for backdrops if Obama needed to address reporters about developments.
Associated Press writer Mark Niesse in Kailua, Hawaii, contributed to this report.