Barack Obama has little time to relax after he triumphed over Republican John McCain, and made history as the first African-American elected the US president - he has to grapple with two wars and a deepening financial crisis.

Aides on Capitol Hill and other Democratic insiders said Wednesday that Obama began the transition by asking Illinois congressman, Rahm Emanuel - a former Clinton White House adviser - to be his White House chief of staff.

Emanuel, 48, who has close ties to Obama's inner circle and is a fellow Chicagoan, was expected to accept the offer, which would make him the main gatekeeper to the Oval Office. A senior Democratic lawmaker, Emanuel, is known for a hard-charging style.

According to one of the Democratic sources, Obama has already launched a transition team, and his aides are "working fast to fill Obama's economic and homeland security teams."

The President-elect's appointments of secretaries of the treasury and defense, national security adviser and other posts are anticipated by the end of this week. The possible secretary of state picks include Sen. John Kerry, D-Mass., retiring Sen. Chuck Hagel, R-Neb., and Democratic New Mexico Gov. Bill Richardson.

Former government officials and public policy experts say such early preparations on the part of Obama are both prudent and necessary given the challenges the US faces amid the Iraq and Afghanistan wars and economic turmoil.

As William Galston, a former domestic policy adviser to Clinton, and now a professor at the University of Maryland, put it: "The need for a seamless transition is greater than it has been in our adult political lifetime."