WASHINGTON - In a Day One burst of activity, President Barack Obama stepped into the Oval Office for the first time as chief executive Wednesday, summoned advisers to begin dealing with war and recession and ordered new ethics rules for "a clean break from business as usual."

Obama also froze salaries for top White House staff, placed calls to Middle East leaders and had aides circulate a draft executive order that would close the notorious Guantanamo Bay prison camp in Cuba within a year.

"The way to make government responsible is to hold it accountable," Obama said as he unveiled ethics rules that he portrayed as the fulfilment of a major campaign promise. He said the action was necessary "to help restore faith in government without which we cannot deliver the changes that we were sent here to make."

In his phone calls to Israeli, Palestinian, Egyptian and Jordanian leaders, Obama emphasized that he would work to consolidate the ceasefire between Israel and Hamas in Gaza, said the new White House press secretary, Robert Gibbs.

Gibbs said Obama expressed "his commitment to active engagement in pursuit of Arab-Israeli peace from the beginning of his term."

A multi-denominational prayer service at Washington National Cathedral and an open house at the presidential mansion were also on the schedule of the 44th president, taking office on a promise to fix the battered economy and withdraw U.S. troops from the unpopular war in Iraq on a 16-month timetable.

The shift in administrations -- former president George W. Bush was back home in Texas -- was underscored in far-off Guantanamo Bay, where a judge granted Obama's request to suspend the war crimes trial of a young Canadian. The judge issued a one-sentence order for the 120-day continuance without so much as a hearing, possibly the beginning of the end for the former administration's system of trials for alleged terrorists.

A draft executive order made clear the new president intends to go further. It called for closing the facility within a year, releasing some of the 245 detainees still there and transferring others to different sites for trial.

Among Obama's executive orders:

-- A freeze on salaries for White House staff earning $100,000 or more -- about 100 people in all.

-- New Freedom of Information Act rules, making it harder to keep the workings of government secret.

-- Tighter ethics rules governing when administration officials can work on issues on which they previously lobbied governmental agencies, and banning them from lobbying the Obama administration after leaving government service.

Obama and first lady Michelle Obama sat in the first row for Wednesday's invitation-only prayer service. Vice-President Joe Biden and his wife, Jill, joined them, as did former president Bill Clinton and Sen. Hillary Clinton, awaiting confirmation as secretary of state later in the day.

"Grant to Barack Obama, president of the United States, and to all in authority your grace and goodwill. Bless them with your heavenly gifts, give them wisdom and strength to know and to do your will," prayed Rev. Andy Stanley, one of numerous clerics from several religions to speak.

Obama's first White House meetings as president meshed with quickened efforts in Congress to add top cabinet officials to the roster of those confirmed on Tuesday and to advance the economic stimulus measure that is a top priority of his administration.

Treasury secretary-designate Tim Geithner, appearing before the Senate Finance Committee for a confirmation hearing, said enactment of the new president's economic stimulus was essential.

He also said the Senate's decision last week to permit use of the second $350 instalment of a financial industry bailout "will enable us to take the steps necessary to help get credit flowing."

He said Obama and he "share your belief that this program needs serious reform."

Geithner also apologized for his failure to pay personal taxes earlier in the decade, calling the omission a mistake. The taxes were repaid in stages, some after an IRS audit and the rest after a review of his returns late last year by Obama's transition team.

Obama and his wife arrived at the White House around 1 a.m. after attending 10 official inaugural balls.

Several hours later he walked into the most famous office in America for the first time as president.

Gibbs, the press secretary, said Obama spent 10 minutes alone and read a note left for him by Bush that was in an envelope marked "To: .44, From: .43."

He was then joined by White House chief of staff Rahm Emanuel and, several minutes later, the first lady.

Wednesday's meeting with economic advisers was coming at a time when 11 million Americans are out of work and millions more feel the loss of savings and face the prospect of foreclosures on their homes.

Democratic leaders hope to have the $825 billion economic stimulus measure to his desk by mid-February.

"Fortunately, we've seen Congress immediately start working on the economic recovery package, getting that passed and putting people back to work," Obama said in an ABC News interview.

"That's going to be the thing we'll be most focused on."

The war in Iraq that he has promised to end featured prominently in Obama's first full day as well.