WASHINGTON (CNN) -- President Obama began his first full day in office with a moment of solitude in the Oval Office, reading a note from his predecessor, before making phone calls to Middle East leaders.

Obama arrived in the Oval Office at 8:35 a.m., according to White House Press Secretary Robert Gibbs. The president spent 10 minutes alone, reading a note left for him in the desk by outgoing President George W. Bush. The note had been placed in an envelope with a note saying: "To: # 44, From: # 43."

White House Chief of Staff Rahm Emanuel met with the president 10 minutes later to discuss the daily schedule, Gibbs said.

Obama called Middle East leaders, according to a senior administration official, including King Abdullah of Jordan, Israeli Prime Minister Ehud Olmert, Palestinian Authority President Mahmoud Abbas and Egyptian President Hosni Mubarak.

On Sunday, Israel and Palestinian militants declared a cease-fire after 22 days of fighting in Gaza.

First lady Michelle Obama joined her husband in the Oval Office at 9:10 a.m., shortly before the first couple departed for the National Prayer Service at the Washington National Cathedral.

President Obama's faith "is a central part of his life and he will begin the first full day of his administration with a service of interfaith prayer and reflection," said Presidential Inaugural Committee Communications Director Josh Earnest.

"The National Prayer Service, which will embody the themes of tolerance, unity and understanding, is a worship service for all Americans."

Later in the day, Obama is expected to meet with his economic team and top brass from the Pentagon. He plans to tell the top U.S. officers that he wants them to plan to have combat forces out of Iraq in 16 months, as he promised during his election campaign, an adviser said.

"It's something he still believes is a responsible timetable," White House adviser David Axelrod told CNN. "But they'll discuss it. Everyone agrees that we need to be on a pace to withdraw our troops, and how that will be implemented I'm sure will be something he'll discuss."

Gen. David Petraeus, whose command oversees U.S. troops in Iraq and Afghanistan, is expected to attend the meeting, CNN learned Tuesday. Petraeus, who will have just arrived from Afghanistan and Pakistan, is expected to brief Obama on the latest developments in the troubled region.

Obama's administration was already in action Tuesday, ordering a 120-day halt to prosecutions of suspected terrorists at the U.S. prison camp at Guantanamo Bay, Cuba, to review the military commissions that try them.

Papers filed at the U.S. prison camp said the request is made "in the interest of justice and at the direction of the president of the United States."

"The judges will receive the requests and review them, and we anticipate a ruling soon," said Cmdr. Jeffrey Gordon, a Defense Department spokesman.

Obama may also launch his plan to reduce greenhouse gas emissions and boost energy independence by requiring an increase in automobile fuel efficiency standards.

The president also is expected to order a reversal of the Bush administration's so-called "Mexico City" policy, which prohibits U.S. money from funding international family planning groups that promote abortion or provide information, counseling or referrals about abortion services.

The 36th anniversary of the Supreme Court's Roe v. Wade abortion ruling is Thursday.

Chief of Staff Emanuel sent a memo to all federal agencies and departments to halt consideration of pending regulations throughout the government until the new staff can examine them, White House officials told CNN.