DES MOINES (AP) - Democrat Barack Obama has been endorsed by the mayor of Iowa's largest city and predicted more criticism ahead from presidential rivals as his political fortunes keep brightening.

Meeting with reporters on Sunday, Obama trotted out Des Moines Mayor Frank Cownie, who last month won a second term. He has focused on global warming and other environmental issues. "Senator Obama has made a promise and is willing an open-minded enough to listen to the mayor of the capital city of Iowa," Cownie said. "Together we can make change in Iowa."

Obama used the event to try to make the case that his approach to global warming and other issues is more innovative than his challengers'.

"I've been talking about how we need a new kind of leadership, and there are few areas where this kind of leader is more urgently needed than climate change," the Illinois senator said. "Year after year, we have seen sound policies and sensible plans crushed under an army of lobbyists. Because of this failure of leadership, the problem now is far worse."

Later, during a rally and fundraiser in Boston, he said his campaign is making a turnaround after some recent doubts.

"I just got back from Iowa, where it appears we're doing pretty good," Obama told a crowd that braved New England's first serious snowstorm. "It's amazing how you go from being D.O.A. to being a genius in about three weeks. But right now, we're going pretty good in Iowa, and we're going pretty good in New Hampshire, because the American people are ready for change and this campaign is about change that you can believe."

On the environment, Obama has released a plan to combat global warming that calls for an 80 percent reduction in U.S. carbon emissions by 2050.

While endorsements traditionally do not play a heavy role in Iowa politics, Cownie has proved a popular mayor. "As many of you know, Mayor Cownie has shown extraordinary leadership on environmental issues," Obama said. "Hopefully, you will give me some tips on how you get 80 percent support. I've got a more modest target in the caucuses."

Obama's central campaign argument against chief rival Hillary Rodham Clinton is that she is too tied to Washington. Clinton has a substantial lead in national polls, but the race for Iowa's leadoff caucuses in January is a virtual dead heat.

As the polls have tightened, the criticism Obama is facing has intensified.

"Those two things are connected, aren't they?" he said. "The folks from the other campaigns are starting to read the polls and getting stressed and starting to issue all kinds of outlandish accusations. What folks need to focus on is all these accusations that are coming seem to correspond to a shift in political fortunes. I suggest that those folks focus on getting their people to caucus for them."

At a rally at Iowa State University in Ames attended by about 400 people, Obama said Democrats should act boldly and take risks. "This party has always been at its best when it's led not with polls, but with principles, a party that America needs us to be right now."