The presidential limousine is parked in front of the south portico of the White House after President Barack Obama and his wife, Michelle, returned from the inaugural balls in Washington early Wednesday. (Charles Dharapak/Associated Press)U.S. President Barack Obama used his first full day in office Wednesday to implement new ethics rules for lobbyists, freeze the pay of some White House employees and pledge increased transparency in government.

The new ethics rules will mean lobbyists are "subject to stricter limits than under any other administration in history," Obama said during a ceremony in the Eisenhower Executive Office Building for swearing in White House staff.

Obama, right, accompanied by Vice-President Joe Biden, speaks in the Eisenhower Executive Office Building in Washington on Wednesday. (Ron Edmonds/Associated Press)Former lobbyists working in government won't be allowed to work on matters for which they lobbied, he said. When they decide to leave government, they'll be barred from lobbying Obama's administration for the length of his presidency.

White House employees earning more than $100,000 US will have their pay frozen at current levels, a measure that will affect about 100 employees.

In a statement, Obama said "families are tightening their belts, and so should Washington."

He also announced a change in policy that will require each federal agency and department to give full attention to freedom of information requests and said he expects members of his administration to be responsive to such pleas.

"There is too much secrecy in this city. Every agency should know … this administration stands on the side of those who seek to make information known.

"Transparency and the rule of law will be the touchstones of this administration," Obama said.

He said the orders he was issuing Wednesday do not go as far as he would like, but that they do go a long way toward "marking a new era" in America.

"Public service is not about advancing you … or your friends. Public service is about … advancing the interests of Americans," he said.

His aides also circulated a draft executive order that would close the detention centre at Guantanamo Bay within a year.

Chief justice re-administers the oath

Obama ended up taking the presidential oath again on Wednesday night in Washington because it was not administered correctly during Tuesday's inauguration ceremony.

The unusual step was taken because John Roberts, chief justice of the U.S. Supreme Court, flubbed the wording of the oath slightly on Tuesday, causing Obama to repeat a version that is different from the one prescribed by the U.S. Constitution.

White House counsel Greg Craig said the retaking of the oath was done as a precautionary measure.

While news of the oath flub made headlines during the inauguration, so too did concerns about Senator Ted Kennedy's health. He suffered a seizure and collapsed during an inauguration lunch event and had to be rushed to hospital.

The 76-year-old senator, who has a brain tumour, was released from hospital on Wednesday. His office said he was kept overnight for observation and is in good spirits.

Mideast peace pledge

Earlier Wednesday, Obama phoned key Mideast leaders to pledge active involvement in peace efforts, the White House said.

Obama called Egyptian President Hosni Mubarak, Israeli Prime Minister Ehud Olmert, Jordan's King Abdullah and Palestinian President Mahmoud Abbas.

"He used this opportunity on his first day in office to communicate his commitment to active engagement in pursuit of Arab-Israeli peace from the beginning of his term, and to express his hope for their continued co-operation and leadership," Robert Gibbs, the new White House press secretary, said in a statement.

The new president started his day early with a prayer service at the National Cathedral. Several hours later, he walked into the Oval Office for the first time as president.

Gibbs said Obama, the country's 44th president, spent 10 minutes alone and read a note left for him by predecessor George W. Bush that was in an envelope marked "To: .44, From: .43."

Obama, whose inauguration drew more than one million people to Washington's National Mall on Tuesday, also held afternoon meetings with his top military and national security advisers.

He was expected to hold an afternoon video teleconference with members of the National Security Council as well as U.S. military commanders in Iraq and Afghanistan. Obama has said he wants combat troops out of Iraq within 16 months, with the aim of shifting his country's military focus to Afghanistan.

During his inauguration address, Obama pledged to "begin to responsibly leave Iraq to its people and forge a hard-earned peace in Afghanistan."

With files from the Associated Press