June 16 (Bloomberg) -- Former Vice President Al Gore endorsed Barack Obama for president, urging fellow Democrats to rally behind the candidate in order to ``change the direction of the country.''

``The outcome of this election will affect the future of this planet,'' Gore, the party's presidential nominee in 2000, told a crowd of about 20,000 people at Detroit's Joe Louis Arena. ``We've got to have new leadership. Not only a new president but new policies.''

Gore had stayed out of the race between Obama and New York Senator Hillary Clinton, who conceded the contest June 7, even as other leading Democrats lined up behind the Illinois senator.

He appeared with Obama tonight in a state that will be a crucial battleground in the general election against Arizona Senator John McCain, the presumptive Republican nominee. Former Senator John Edwards of North Carolina, who ended his own bid for the Democratic nomination earlier this year, also gave his endorsement to Obama in Michigan last month.

Gore will help Obama with independents and environmentalists in states, such as Michigan, where Obama spent little or no time during the primary season, said Julian Zelizer, a history and public affairs professor at Princeton University in New Jersey.

``A lot of Michigan voters now know Barack Obama but announcements from these kinds of figures just gives a little more attention to the candidate,'' Zelizer said.

Campaign With `Respect'

Gore called on the party to conduct a general election campaign ``in a spirit of respect for the Republican nominee.'' When a smattering of boos erupted from the audience, Gore said, ``I'm glad I brought it up.''

While praising McCain for supporting action to combat global warming and his record of service, Gore said he would keep in place many of the policies of President George W. Bush.

``We must, and we will, make our case that America cannot afford a continuation of the policies of the last eight years,'' said Gore, the vice president in Bill Clinton's administration.

Like Obama, Gore opposed Bush's decision to go to war in Iraq.

Obama thanked Gore for his support, his service to the country and for ``everything that he is doing to ensure that we leave a planet that is better for our children.''

Role for Gore

``When I am president I will be counting on Al Gore to help me lead the fight for a clean energy future here in America and around the globe,'' Obama said.

Since losing the presidency to Bush in 2000 after the U.S. Supreme Court halted a recount of votes in Florida, Gore, 60, has campaigned to raise awareness of the effects of global warming. He won the Nobel Peace Price in 2007 for those efforts.

Gore announced he'd be appearing with Obama today in a fundraising e-mail to supporters. His involvement in Obama's campaign provides an even broader donor base, said Kenneth Goldstein, a political science professor at the University of Wisconsin in Madison.

``The big effect is for fundraising,'' Goldstein said. ``Gore encouraging his supporters to give to Obama provides even more funds -- raised with low overhead -- to an already incredibly well funded Obama operation.''

Before his appearance at the arena, Gore introduced Obama at a fundraiser at a Detroit hotel.

Good Advice

Obama said earlier today that he and Gore spoke throughout the primary campaign about issues such as the environment. Gore provided some ``good political advice'' as well, Obama said.

``He's somebody who has been a visionary not just for the party, but for the country,'' Obama, 46, said in Flint, Michigan, as he shook hands with workers outside a General Motors Corp. engine plant.

Obama's campaign today also began filling jobs in the roster for the general election, naming Patti Solis Doyle, Clinton's onetime campaign manager, as the designated chief of staff for Obama's vice presidential nominee. Solis Doyle was fired in February after Obama won a series of primary and caucus victories.

Among other appointments, Stephanie Cutter, a spokeswoman for Senator John Kerry's 2004 presidential campaign, was named a senior adviser and chief of staff to Michelle Obama, the candidate's wife.

To contact the reporter on this story: Julianna Goldman in Detroit at jgoldman6@bloomberg.net

Last Updated: June 16, 2008 22:33 EDT