Washington - Senators Barack Obama and John McCain both mentioned billionaire investor Warren Buffett as a qualified person to head the US Treasury Department in the next administration.

The Democratic and Republican presidential candidates faced off at Belmont University in Nashville, Tennessee, in their second debate amid what Obama called "the worst financial crisis since the Great Depression."

They were surrounded by 80 undecided voters who had submitted written questions, which were screened by the moderator in a so- called town hall meeting format.

With global stock markets continuing their downward spiral this week, one questioner wanted to know who both candidates would choose for their secretary of the treasury to lead the country out of the finance crisis.

McCain immediately cited Buffett, 78, chief of Berkshire Hathaway, an insurance conglomerate and holding company with investments across numerous industries. The low-key Buffett, whose investment decisions are closely followed on Wall Street, is often referred to as the Oracle of Omaha, the Nebraska city where he was born and still lives.

Forbes magazine this year estimated Buffett as the richest man in the world with a net worth of 62 billion dollars. Buffett has announced plans to donate 30 billion dollars to charity.

Last month, Berkshire Hathaway bought at 5-billion-dollar stake in top investment bank Goldman Sachs. The action was seen as Buffett's endorsement of the firm as it tries to stabilize itself during the ongoing credit crisis that has already claimed several top US financial firms.

Buffett is a strong supporter of Obama, who agreed Tuesday night that Buffett would be a strong treasury secretary.

McCain also named Meg Whitman, former chief executive of online auction site eBay, as a possible treasury secretary. She is a McCain supporter and campaign advisor.