President Barack Obama took time out of a quiet Christmas with family, friends and basketball to greet service men and women during their Christmas dinner on the Marine Corps Base Hawaii this afternoon.

The unannounced visit happened at about 3:30 p.m. Obama visited with service members at the same base at about the same times during his last two visits.

The president, along with his wife, Michelle Obama, spent more than half an hour shaking hands and hugging service members who had arrived for Christmas dinner at the mess hall at Marine Corps Base Hawaii.

With U.S. troops serving in Afghanistan, Iraq and other outposts around the world, the Obamas also used the president’s weekly radio and Internet address to encourage Americans to find ways to support service members during the holiday season.

"Let’s all remind them this holiday season that we’re thinking of them, and that America will forever be here for them, just as they’ve been there for us," the president said.

Mrs. Obama , who has made working with military families one of her top priorities as first lady, said Americans don’t need to be experts in military life in order to give back to those who serve their country. She urged the public to reach out through their schools and churches, or volunteer with organizations that support military families.

"Anybody can send a care package or pre-paid calling card to the front lines, or give what’s sometimes the most important gift of all: simply saying thank you," Mrs. Obama said.

Vice President Joe Biden and his wife, Jill, spent Christmas in Washington, where they visited wounded soldiers and their families at Walter Reed Army Medical Center.

The public appearance contrasts with the rest of the president’s Christmas Day, spent at a luxurious oceanfront home in Kailua with his wife, Michelle, and daughters Malia and Sasha. The first family celebrated Christmas with a small circle of friends and family, including some of Obama’s childhood friends and the president’s sister, Maya Soetoro-Ng, who lives here on Oahu, the island where Obama was born and spent much of his childhood.

The Obamas dined on steak, roasted potatoes, green beans and pie, and the sports-obsessed president got a chance to relax and watch some NBA basketball.

The president’s Christmas was been far quieter than last year’s holiday, when a 23-year-old Nigerian man allegedly attempted to blow up a plane bound for Detroit. The incident raised questions about the nation’s terror readiness and consumed the rest of Obama’s vacation.

Thus far, Obama’s excursions in Hawaii have been mostly to the gym and golf course. On Christmas Eve he visited the beach with his daughters.

Mrs. Obama skipped the beach so she could give some lucky children a Christmas surprise. The first lady answered calls for the "Tracking Santa" program, a Christmas tradition run by the North American Aerospace Defense Command, or NORAD. With help from NORAD’s Santa Route Schedule, Mrs. Obama was able to tell children Santa’s whereabouts as he made his Christmas Eve rounds.

The first family has no public events planned during their vacation. The president, though, is receiving daily briefings, beginning work on January’s State of the Union address and evaluating a staff review headed by interim chief of staff Pete Rouse.

Obama arrived in Hawaii on a high note, having secured victories on legislative priorities: ratification of a nuclear arms treaty with Russia and the repeal of the military’s ban on gay service members. He also compromised with Republicans to extend tax cuts for all income earners, a deal that angered some liberals but won him rare bipartisan support.

Awaiting Obama in 2011 is an economy still struggling to achieve steady growth, a divided Congress and a host of Republicans ready to run for his job in the 2012 election.

The Obamas are expected to stay in Hawaii through Jan. 2.