Washington - Democrat Barack Obama and Republican John McCain began their first presidential debate Friday night in a discussion that was largely expected to focus on foreign policy.

But the two candidates are expected to also hear questions about the financial crisis in the United States and President George W Bush's 700-billion-dollar rescue plan.

Moderator Jim Lehrer, a long-time news anchor for the Public Broadcasting System, said that the topic of foreign policy "by definition includes the global financial crisis."

The debate had been scheduled for weeks, but it remained uncertain until midday Friday that it would take place. McCain, 72, had suggested on Wednesday that he would not attend so that he could stay in Washington to work on legislation to address the financial crisis.

Obama, 47, rejected McCain's request to postpone the debate at the University of Mississippi in Oxford, Mississippi.

The debate is the first of three scheduled before the November 4 election.

McCain is regarded as more experienced when it comes to foreign policy, while Obama has more voter confidence when it comes to the economy, polls show.

A weak performance by McCain on the subject of foreign policy could cost him his strongest asset in the minds of voters. (dpa)