Washington: “Ending one journey to begin another”, President-elect Barack Obama on Monday officially quit the US Senate to concentrate on assembling his core team that will serve him in his historic journey to the White House.

By resigning from the Senate, the 47-year-old first-time Democratic Senator from Illinois, who defeated his Republican rival John McCain in the 4 November presidential election, has removed himself from any official role in the lame-duck session of Congress that will convene this week.

Obama announced his resignation from the Senate in a letter published in Illinois newspapers, telling his constituents, “I will never forget, and will forever be grateful, to the men and women of this great state who made my life in public service possible”.

Observing that he is “ending one journey to begin another”, Obama said that he is stepping down “to prepare for the responsibilities I will assume as our nation’s next president”.

Obama will be sworn-in as the 44th President of the United States on 20 January, 2009.

Illinois Governor Rod Blagojevich has said he will appoint a replacement senator by the end of the year.

Meanwhile, Obama has also laid more groundwork for the start of his administration by deciding on additional members of his senior staff, including a White House counsel, as he prepared to meet with Senator McCain at his transition office in downtown Chicago.

The meeting comes days after Obama sat down separately with Senator Hillary Rodham Clinton and New Mexico Governor Bill Richardson, both of whom opposed him in the Democratic primaries.

Obama has not yet announced any Cabinet selections, although the meetings with Clinton and Richardson triggered speculation that one was imminent, since both are said to be on his shortlist for secretary of state.

While Congress debates how best to help the economy, Obama is expected to continue building his governing team in the coming days, Washington Post reported.

Yesterday, Obama made some top-tier appointments to the White House. Washington lawyer Gregory B Craig will be White House counsel, it said, quoting a person involved in the transition.

Craig had defended Bill Clinton against impeachment charges. During the campaign, Craig became a close adviser to Obama, and he served as the stand-in for McCain during debate preparations.

Obama’s Senate chief of staff, Peter M Rouse, was officially announced as a senior White House adviser. Two deputy chiefs of staff were also announced: Jim Messina and Mona K Sutphen.

Thus far, Obama’s selections have been mostly a mix of Washington veterans — many with ties to the Clinton administration — and trusted campaign aides. Late last week, the president-elect named close friend and adviser Valerie Jarrett as a senior White House aide. Campaign strategist David Axelrod will also hold a senior advisory role.