Barack Obama is expected to dampen the euphoria of his supporters today as he starts to square soaring campaign rhetoric with the grim realities waiting for him in the White House.

He will make his first public appearance in more than 48 hours for a press conference in Chicago. On Monday he will travel to Washington for talks on the two-month transition with President Bush, who has promised to help him “hit the ground running”.

Speaking on the South Lawn of the White House, Mr Bush said: “We face economic challenges that will not pause to let a new president settle in.”

The President has previously voiced fears that the US is particularly vulnerable to a terror attack or a national security crisis during the transition. Last night it was disclosed that the FBI had alerted Mr Obama and John McCain about an unspecified foreign organisation that had successfully hacked into their campaigns’ computer files during the election.

Mr Obama received his first intelligence briefing since becoming President-elect from the CIA. He also spoke on the telephone with world leaders. Gordon Brown got ten minutes, President Sarkozy is said to have received a full half hour and there was also a conversation, of undisclosed length, with the outgoing Israeli Prime Minister, Ehud Olmert.

Yesterday he completed the appointment of Rahm Emanuel as his White House Chief-of-Staff, while campaign strategist David Axelrod and Valerie Jarrett, an aide, are being lined up for roles as senior presidential advisers.

On Tuesday night Mr Obama spoke of a “steep climb” ahead and how he may not achieve all he wants in a first term. In interviews he has asked not to be judged by the traditional yardstick of his first 100 days so much as his first 1,000 days or even more.

Spokesman Robert Gibbs, who is likely to be made White House press secretary, said: “It’s important that everybody understands that this is not going to happen overnight. There has to be a realistic expectation of what can happen and how quickly.”

The sober tone Mr Obama adopted in his speech on election night was intended to be the first of many signals that some of the promises he made during a 21-month election campaign may be difficult to fulfil quickly.

His first task is to fill more than 7,000 political appointments in the White House and his administration — 1,200 of which will need Senate confirmation — without breaching a pledge to end the “revolving door” between government and lobbyists.

According to his campaign promise, no one will be allowed to work on regulations or contracts “directly and substantially related” to past lobbying work for two years. Washington is a city where many policy experts are often hired by lobbying firms when they leave government. Questions are being raised over whether John Podesta, who heads the team, is in breach of the strict ethics rules. While not a registered lobbyist, Mr Podesta has lobbied in the past on issues including Pentagon spending and energy issues. His brother also runs a lobbying firm that the two founded.

Even without lobbyists Mr Obama faces a clamour from special interest groups and a Democratic-dominated Congress, as well as tens of millions of voters who want him to end the Bush years abruptly. For instance, unions — which contributed $400 million (£256 million) and an army of volunteers to Democratic election efforts — are pushing for legislation scrapping secret ballots in workplaces.

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