DENVER - FORMER President Bill Clinton's mythic political skills face a major test when he takes the rostrum at the Democratic convention on Wednesday, looking past his disappointment - some say anger - to speak in support of Barack Obama, the man who ended Hillary Rodham Clinton's run for the White House.

Hillary Clinton passed the same test on Tuesday night with a soaring rhetorical paean to her own historic run to be America's first woman commander in chief and a convincing call for her still-angry backers to unify behind Mr Obama, whose victory would make him the first black US president.

While Bill Clinton's speech on the third night of the convention will only be a courtesy accorded former presidents, Mr Obama - who speaks on Thursday, the last night of the convention - needs his support desperately.

And there were fears Mr Clinton, one of the finest political orators of a generation, would overshadow Mr Obama's vice presidential running mate Sen. Joe Biden, who closes out Wednesday's session.

Bill Clinton, who showed flashes of anger over what he felt were unfair attacks on his wife during the Democratic primaries, has given Mr Obama only tepid support since Hillary Clinton ceded to Mr Obama in the close and hard-fought battle for the party's nomination in June. The ex-president was to speak shortly after his wife's name was symbolically placed in nomination - a nod to the New York senator's strong bloc of delegates who will be in the hall here in Denver, many of them still itching for a fight.

There were fears in the Obama camp, which felt obliged to allow Mrs Clinton's pro forma nomination, that the floor demonstration for his vanquished rival could be a blot on the party's hopes of showing a unified front against the Republicans and their resurgent candidate, John McCain.

Meanwhile, Mr McCain was contending in a new TV ad that Obama was 'dangerously unprepared' for the White House when he described Iran as a 'tiny' nation that didn't pose a serious threat.

'Iran. Radical Islamic government. Known sponsors of terrorism.

Developing nuclear capabilities to 'generate power' but threatening to eliminate Israel,' says the ad, which was being run in key states.

'Terrorism, destroying Israel - those aren't 'serious threats''? Missing from the ad was the context of Mr Obama's remarks last May in which he compared Iran and other adversarial governments to the superpower Soviet Union. 'They don't pose a serious threat to us the way the Soviet Union posed a threat to us,' he said in arguing for talks with Iran. 'You know, Iran, they spend one-100th of what we spend on the military. If Iran ever tried to pose a serious threat to us, they wouldn't stand a chance.'

The McCain ad signaled a shift from trying to stir up Hillary Clinton's supporters with her primary-season criticism of Obama, which the former first lady has since replaced with glowing support for the Democratic candidate. -- AP