Denver, Colorado - Michelle Obama stole the limelight and apparent affection of Democratic delegates Monday night, describing husband Barack Obama as a persistent suitor in their courting days who would carry the same kind of determination into the White House.

Her 20-minute speech, the headliner of the opening night of the four-day presidential nominating convention, aimed to raise the personal profile of a man who was little known nationally until four years ago.

She also stroked the emotions of supporters of her husband's chief rival for the Democratic nomination, Hillary Clinton, who carried more than 18 million votes and 40 per cent of the delegates in primary elections.

Clinton had "put those 18 million cracks in the glass ceiling, so that our daughters and sons can dream a little bigger and aim a little higher," Obama said.

Her audience was ready to keep cheering at the Clinton remark but was cut short when she continued the speech - a pattern she followed at other points in her address when delegates were prepared to cheer much longer.

In the live broadcast to the country, Obama described the sort of working-class background she and her 47-year-old husband share that could echo strongly with average Americans when they compare the candidate to his presumptive rival, Republican John McCain.

McCain, 71, is in his second marriage to a beer distributor heiress, and joined the military on the strong legacy of a father and grandfather who were four-star navy admirals and part of the military aristocracy.

After the speech, Barack Obama's image loomed up on the video screens on a videophone connection from Kansas City, where he watched his wife with a family he met on the campaign trail.

Referring to the tale of how he was an intern in Michelle's law office who kept getting rejected when he asked her out, Obama said the story showed he would be a "persistent president."

Children Malia, 10, and Sasha, 7, joined their mother on stage for the phone-in from dad.

"How do you think mom did?" the candidate asked.

"I think she did good," Sasha replied. "I love you daddy, bye." (dpa)