Obama promises speech with purpose, no mere rhetoric

US Democratic presidential candidate Senator Barack Obama (D-IL) speaks at a campaign event at the Mississippi Valley Fairgrounds in Davenport, Iowa, August 25, 2008.

MOLINE, Illinois (Reuters) - Barack Obama promised on Monday to accept the U.S. Democratic presidential nomination with a "workman-like speech" offering policy details and not simply his trademark rhetoric.

Critics who admire his oratorical gifts say he needs to match lofty words with specifics. They say it isn't enough for him to promise change and hope without spelling out how he intends to do that if elected on November 4.

"I'm not aiming for a lot of high rhetoric. I'm much more concerned with communicating how I intend to help middle-class families live their lives," Obama told reporters in Illinois as he made his way through key states on his way to the Democratic convention in Denver where he will speak on Thursday.

Obama burst onto the national U.S. political stage with a rousing speech at the 2004 Democratic convention in which he used his mixed-race heritage to call for political and racial unity across the country.

"People know that I can give the kind of speech that I gave four years ago. That's not the question on voters' mind. I think they're much more interested in, what am I going to do to help them in their lives?" he said.

"And so, in that sense, this is going to be a more workman-like speech."

MCCAIN MOCKS OBAMA RHETORIC

Republican rival John McCain, whose party convention follows the Democrats next week, has seized on Obama's rhetorical talents to mock him as a celebrity who is light on substance.

Obama's autobiographical books "Dreams from My Father" and "Audacity of Hope" became bestsellers after the 2004 speech. Other Democratic candidates were eager to have Obama join them on the campaign trail.

When that year he was elected to the U.S. Senate from the Midwestern state of Illinois, a buzz spread about his potential as a presidential candidate. If he wins, Obama would be the first black U.S. president.

Obama has put in long hours preparing and polishing his speech, working late into the night as he often does. He said he viewed his acceptance speech this week in a very different light from the 2004 speech.

"You know, 2004 I think was unique. Nobody knew who I was and I think even up to the time that I walked onto the stage and we had handed out Obama signs, people were thinking, what is this?" he said.

In an apparent bid to lower expectations, he said: "I don't think you can duplicate that kind of moment."

The speech coincides with the 45th anniversary of civil rights leader Martin Luther King Jr.'s "I Have a Dream" speech delivered on the steps of the Lincoln Memorial in Washington.

Obama sidestepped a question about whether he would refer to that on Thursday but said King's speech was a "seminal moment" in U.S. history and a reminder of the progress the country has made on race relations.

"I think it's fair to say that had it not been for, not just for the speech but the movement behind the speech -- the sentiments behind the speech, the work and toil and the risks that were taken by previous generations -- then I wouldn't be in Denver on Thursday accepting the nomination for the presidency," he said.

(Editing by Patricia Wilson and David Storey)