* Former U.S. president speaks at convention Wednesday night
* Clinton tenure marked by peace and U.S. economic growth
* Democrat is popular with large cross-section of Americans
CHARLOTTE, N.C., Sept 5 (Reuters) - The 1988 Democratic convention introduced Bill Clinton to the nation as a long-winded bore. The 2012 convention may cement his status as his party's most valuable weapon.
In his debut on the national stage, the young Arkansas governor didn't exactly electrify the party faithful, who cheered loudest when he said, "In closing ..." toward the end of his 35-minute speech.
This time around, it's safe to say that few in the convention audience will be eager for Clinton to wrap it up.
At their convention on Wednesday night, Democrats are counting on the former president to explain to voters how their lives would improve if they give President Barack Obama another four years in the White House - a tricky argument to make in a time of rising poverty, high employment and sluggish economic growth.
As a president who oversaw a growing economy and balanced budgets, Clinton is a particularly effective salesman for Democrats' economic ideas, they say.
His ability to sugarcoat attacks and explain complicated ideas in terms that voters can understand also will make him a valuable player in the bitter, jobs-focused battle between Obama and Republican Mitt Romney, they say. And Clinton can be an effective ambassador to groups that have been resistant to Obama's charms, from working-class whites to wealthy donors in the financial industry.
"It's entirely possible that Clinton will make the case for Obama better than Obama has ever made for himself," said former Clinton adviser William Galston.
Clinton's public stature has grown steadily since he left office at the beginning of 2001. With an approval rating of 66 percent, according to Gallup, he enjoys popularity among all segments of the American public.
Nearly half of Republicans in the poll give him high marks, which perhaps accounts for the gentle treatment he has received from Republican presidential candidates.
Romney called Clinton's program that required welfare recipients to get jobs a "great accomplishment."
Another Republican, former House Speaker Newt Gingrich, bragged that he worked with Clinton to balance the budget in the 1990s. He spent less time bragging about the budget battles that led to two government shutdowns, or the divisive effort to impeach Clinton in the aftermath of a sex scandal.
The conservative Wall Street Journal editorial page noted that the prosperity that the United States enjoyed on Clinton's watch gives him added weight when attacking Republicans on economic topics. "The payoff for putting Mr. Clinton center stage at the 2012 convention ... could be big," the paper wrote on Tuesday.
After more than a decade of war and recession, voters are more likely to think of Clinton's time in office from 1993 to 2001 as an era of peace and growth rather than sex scandals and government shutdowns, said Democratic pollster Stan Greenberg.
"People think of the 1990s as a prosperous period for the country," he said.
NOT ALWAYS BEST BUDDIES
Before he won the presidency, Obama did not always look on the Clinton era favorably.
As a state senator, Obama spoke out against Clinton's welfare changes. As a presidential candidate, Obama questioned Clinton's accomplishments during heated primary battles against Clinton's wife, Hillary, that left lingering bitterness on both sides.
Since then, the two have managed to form what Democrats describe as a solid working relationship with both Bill and Hillary, who has won high marks as Obama's secretary of state.
"I think that over the four years of the Obama presidency, the tension that existed receded and real admiration took its place," sa id John Podesta, a former Clinton chief of staff with close ties to the Obama administration.
Clinton has praised Obama's economic policies and helped him raise campaign money, but he occasionally has strayed off script. He criticized Obama's attacks on Romney's business career this year and questioned Obama's plan to let income tax rates rise for wealthy households.
Even now, the Obama campaign isn't quite sure what Clinton is going to say.
"He's working on his remarks and I'm sure when he's done we'll see them," Obama campaign spokeswoman Jen Psaki told reporters aboard Air Force One on Tuesday.
Clinton has appeared in a television ad for the Obama campaign, and campaign officials say he's going to play a significant role in the weeks leading to the Nov. 6 election.
Democrats say Clinton is especially effective speaking to white working-class voters, a group that has been especially resistant to Obama, the nation's first African American president. Obama is unlikely to win a majority of these voters, but he will have to limit his losses in order to win in November.
"The appeal of Bill Clinton is, he really talks to those folks who are out there working for a living," said South Carolina state Senator Vincent Sheheen.
Democrats say Romney missed an opportunity to lay out a detailed job-creation plan in his convention speech last week. They expect Clinton and other convention speakers to detail how voters' lives would improve over the coming four years if they re-elect Obama.
"He may very well be saying the basic themes of the convention, but he'll do it in a manner that really connects with people," said Susan Ness, a Democratic delegate from Maryland who has known Clinton for more than 25 years.