U.S. Democrats ready celebration for Obama

By John Whitesides, Political Correspondent

DENVER (Reuters) - Democrats prepared a grand celebration on Thursday for Barack Obama, who will accept a historic presidential nomination with a speech that spells out his vision for change in America.

Obama, the first black presidential nominee of a major U.S. party, will deliver the address in Denver's open-air football stadium before 75,000 supporters on the 45th anniversary of Martin Luther King's "I Have a Dream" speech -- a landmark in the U.S. civil rights movement.

The televised speech by Obama, who was formally nominated on Wednesday, will give the first-term Illinois senator his biggest national audience until he meets Republican rival John McCain in late September in the first of three face-to-face debates before the Nov. 4 election.

In an unannounced appearance in the hall at the end of Wednesday's national convention program, Obama said he shifted the event to the football stadium as a tribute to the grass-roots energy of his supporters.

"We want to open up the convention to make sure that everybody who wants to come can join in the party," said Obama, 47, who appeared on stage after the acceptance speech of his newly minted running mate, Delaware Sen. Joe Biden.

National conventions are often the first time voters start to pay attention to a presidential race. Opinion polls show many voters are still unfamiliar with Obama and concerned about his readiness for the job.

Speakers at the convention have tried to address those concerns, led by rousing testimonials for Obama from former rival Hillary Clinton, her husband former President Bill Clinton and Biden.

"Barack Obama is ready to lead America and to restore American leadership in the world," Bill Clinton told flag-waving Democrats, answering a frequent line of Republican attack.