Aug. 27 (Bloomberg) -- Hillary Clinton asked her supporters last night to put aside any idea of voting for Republican John McCain and instead back her former rival for the Democratic presidential nomination, Barack Obama.

``Whether you voted for me, or you voted for Barack, the time is now to unite as a single party with a single purpose,'' Clinton said at the Democratic National Convention in Denver. Americans can't afford another Republican in the White House, she said: ``No way. No how. No McCain.''

Clinton's speech took the spotlight away from a keynote address delivered by former Virginia Governor Mark Warner. She designed it as an appeal to the millions of people who backed her during the primaries, and sought to quiet talk of discord between the two camps.

Greeted with several minutes of a standing ovation and white ``Hillary'' signs that covered the arena, Clinton began by saying she was ``a proud supporter of Barack Obama,'' bringing the audience once again to its feet. ``Barack Obama is my candidate, and he must be our president,'' Clinton said.

The attention today will turn to Clinton's husband, former President Bill Clinton, who will speak to the convention. In addition, Hillary Clinton's delegates will place her name in nomination at a roll call. The idea is to give her supporters a voice before Obama becomes the party's official nominee.

In a USA Today/Gallup poll released yesterday, 16 percent of registered Democrats who backed Clinton in the primaries said they would support McCain for president.

Carrying on the Fight

Clinton, 60, a New York senator, told delegates that Obama would carry on her 35-year fight for affordable health care for all Americans, her quest to rebuild the middle class and her efforts to ``stand up for all those who have been invisible to their government for eight long years.''

The speech ``was terrific and helps unify the party behind Obama,'' said James Thurber, a political science professor at American University in Washington. Her humor and politics also hit the mark, he said. ``She had message discipline that helped the ticket.''

David Redlawsk, a University of Iowa professor who attended the convention as a delegate for former candidate John Edwards, said he was impressed with Clinton, who was his third choice for president. ``It was a home run, clear and simple,'' he said.

Unity

As Clinton spoke last night, volunteers handed out two sets of blue signs to add to the original white ``Hillary'' placards. Some said ``Hillary'' and some said ``Obama.'' The other side of both signs said ``Unity.''

Obama, who arrives in Denver this afternoon, watched Clinton's speech at a small house party in Billings, Montana. The Illinois senator sat on the edge of a couch and let out a big laugh when Clinton thanked her supporters, calling them ``the sisterhood of the traveling pantsuits.''

Obama, 47, clapped after several lines, including Clinton's call for better care of U.S. veterans. ``That was a strong speech,'' he told the guests. ``It laid out the case.''

Obama called Clinton after her speech to express his gratitude, his spokesman Robert Gibbs said. He told Clinton she gave a terrific speech and that he was moved by her video introduction. He also called Bill Clinton to say how good he thought his wife's speech was.

Hillary Clinton paid tribute not only to Obama, but to his wife, Michelle, who spoke the previous evening, and Obama's newly chosen running mate, Delaware Senator Joseph Biden, who will address the convention tonight.

Pumping Energy

``It was a speech that pumped energy into the convention after a first day that was more family than fire,'' said Stephen Hess, a scholar at Washington's Brookings Institution. ``If Biden can attack forcefully'' today, and ``Obama can take us to the mountaintop on Thursday, the Democrats will have done all that a convention is supposed to do.''

The speech capped two days of events designed to honor Clinton's accomplishments, some sanctioned by the former first lady and others not.

Yesterday afternoon, about 250 Clinton supporters spent about an hour marching in her honor, toting campaign signs. There was little rancor in the crowd, which moved peacefully through downtown Denver.

Clinton also addressed two groups designed to promote the candidacies of women yesterday. At one, Emily's List, she told a crowd of more than 2,500 to ``work as hard for Barack Obama as you did for me.''

Overblown?

Some of her supporters said the talk of discord in the party was overblown.

``Reports of disunity have been greatly exaggerated,'' said Sara Gelser, 34, an Oregon delegate who will back Clinton on the first roll call. After that, ``I will be fully on board'' for Obama, she said. Her fellow Oregon delegate, Joan Demarest, 38, agreed, holding up a ``Hillary supporter for Obama'' button.

Warner previewed the attention that would be paid to Clinton during his own address, noting that it was ``daunting'' to deliver the keynote speech that Obama gave four years earlier and to speak ``before Hillary Clinton.''

The former governor and Senate candidate focused his speech on the U.S.'s economic challenges and told delegates the country faces the most important contest of a generation, which ``won't be won with yesterday's ideas and yesterday's divisions.''

Warner encouraged the use of American innovation to address high gas prices and global warming. He said American workers can compete with anyone in the world.

``With the right leadership we can once again achieve a standard of living that is improved and not diminished in each generation,'' he said.

To contact the reporters on this story: Kristin Jensen in Denver at kjensen@bloomberg.net; Catherine Dodge in Denver at cdodge1@bloomberg.net

Last Updated: August 27, 2008 00:34 EDT