(AP) - President Barack Obama stepped into the Oval Office for the first time as chief executive on Wednesday and summoned economic advisers and top military officials to separate meetings aimed at delivering the change he promised as a candidate.

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, who took 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.

Obama's first public act in office was to institute new limits on lobbyists in his White House and to freeze the salaries of high-paid aides, in a nod to the country's economic turmoil.

Announcing the moves while attending a ceremony in the Eisenhower Executive Office Building to swear in his staff, Obama said the steps "represent a clean break from business as usual."

The pay freeze, first reported by The Associated Press, would hold salaries at their current levels for the roughly 100 White House employees who make over $100,000 a year. "Families are tightening their belts, and so should Washington," said the new president, taking office amid startlingly bad economic times that many fear will grow worse.

Those affected by the freeze include the high-profile jobs of White House chief of staff, national security adviser and press secretary. Other aides who work in relative anonymity also would fit into that cap if Obama follows a structure similar to the one George W. Bush set up.

Obama's new lobbying rules will not only ban aides from trying to influence the administration when they leave his staff. Those already hired will be banned from working on matters they have previously lobbied on, or to approach agencies that they once targeted.

The rules also ban lobbyists from giving gifts of any size to any member of his administration. It wasn't immediately clear whether the ban would include the traditional "previous relationships" clause, allowing gifts from friends or associates with which an employee comes in with strong ties.

The new rules also require that anyone who leaves his administration is not allowed to try to influence former friends and colleagues for at least two years. Obama is requiring all staff to attend to an ethics briefing like one he said he attended last week.

Obama called the rules tighter "than under any other administration in history." They followed pledges during his campaign to be strict about the influence of lobbyist in his White House.

"The new rules on lobbying alone, no matter how tough, are not enough to fix a broken system in Washington," he said. "That's why I'm also setting rules that govern not just lobbyists but all those who have been selected to serve in my administration."

In an attempt to deliver on pledges of a transparent government, Obama said he would change the way the federal government interprets the Freedom of Information Act. He said he was directing agencies that vet requests for information to err on the side of making information public - not to look for reasons to legally withhold it - an alteration to the traditional standard of evaluation.

Just because a government agency has the legal power to keep information private does not mean that it should, Obama said. Reporters and public-interest groups often make use of the law to explore how and why government decisions were made; they are often stymied as agencies claim legal exemptions to the law.

Obama calls for a remaking of America The inauguration of Barack Obama