Copenhagen - As President Obama prepared to visit the historic climate conference here, there were signs Wednesday of a break in the impasse between rich and developing nations.

The United States and Japan agreed to make major contributions to the developing world to keep a deal alive. And the leader of a bloc of African nations said they would accept a smaller - though still sizable - package of financial aid in return for going along with an agreement.

But tear gas hung in the air outside the conference center as protesters demanding faster and more stringent cuts in greenhouse-gas emissions clashed with police. And inside, talks were slowed by disagreements within the developing world - which has proved an unexpectedly powerful and fractious force.

Some environmentalists expressed hope that Obama's appearance Friday, the final day of the 12-day talks, could help conclude these two chaotic weeks with a global deal.

"If the pieces are here, President Obama is the only person who can pull them together into an agreement," said Fred Krupp, president of the Environmental Defense Fund. "We expect him to do so."

Even before the United Nations-led talks began, it was clear they would not deliver what environmental groups had initially hoped for: a global treaty on climate change, with high-emitting countries formally pledging to reduce their greenhouse-gas emissions in the coming decades.

Instead, the goal was to sign a "political agreement," in which nations would pledge to tackle emissions but without making a binding commitment under international law. The understanding was that a formal treaty would come in 2010.

That goal still seemed within reach Wednesday, one day before Secretary of State Hillary Rodham Clinton arrives to take part in the negotiations.

White House press secretary Robert Gibbs told reporters that it is typical of global conferences that some differences remain when heads of state arrive. Obama, who has made phone calls this week to the leaders of developed nations such as Germany and France and developing countries such as Bangladesh and Ethiopia, will join 118 other world leaders in the Danish capital.

"I think you've seen in some ways people say that ... some of this is just going to get hashed out when leaders of these countries get here to start hashing it out," Gibbs said. "I think that's in many ways how some of this stuff happens. And I don't think that, in all honesty, that'll be a lot different here."

In a moment that distilled the diplomatic dance in Copenhagen, Ethiopian Prime Minister Meles Zenawi - who is representing all of Africa here - unveiled his proposal Wednesday for a system in which rich countries would provide money to poor ones to help deal with the effects of climate change. These effects might include rising sea levels, droughts and changing rainfall patterns.

Zenawi said he would accept $30 billion a year in the short term, rising to $100 billion a year by 2020, for poor countries worldwide. This was seen as a key concession by developing countries, who previously spurned that figure - originally proposed by European countries - as too low.

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"It is no exaggeration that this is our best, and perhaps our last, chance to save our planet from destructive and unpredictable change," Zenawi said. "If we fail to rise above the current challenge of climate change, we will then have proved that global economic progress is based on a fundamentally dysfunctional political system."

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Also Wednesday, Japanese officials said their country would provide $15 billion over the next three years to help impoverished countries adapt to climate change and lower emissions. But that offer would be good, State Secretary for Foreign Affairs Tetsuro Fukuyama said, only if a global agreement is reached this week.

"We have to move forward," Fukuyama said in an interview. "We have to have an agreement."

The United States has yet to say how much money, if any, it will offer to poor countries for this purpose. But on Wednesday, Agriculture Secretary Tom Vilsack announced $1 billion in U.S. funding aimed at helping developing countries preserve their forests.

"These types of announcements are exactly what's needed to build trust for an ambitious outcome by the end of the week," said Andrew Deutz, who directs international climate policy for the Nature Conservancy.

Wednesday's progress was mainly concerned with just one of the conference's sticking points: how much the rich should pay the poor. On other questions - including to what extent industrialized and major developing countries should reduce their emissions, and how to include these pledges in a global pact - the talks only inched forward.

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On Wednesday, for instance, rich and poor countries were disagreeing about the starting point for that debate.

The European Union, Japan, Australia, Russia and Canada want to scrap the 1997 Kyoto Protocol, because the United States and China did not join in its pledges to cut emissions, and start with a new document. But a bloc of poorer countries wants to make the next agreement a formal sequel to the one in Kyoto, which binds most developed countries to emission cuts and provides some financing for poor ones.

On Wednesday, many developing countries walked out of negotiations over that disagreement. Selwin Hart, a delegate from Barbados and a member of what the United Nations calls the Group of 77, which actually includes 130 countries, said the Kyoto deal offers "legal certainty" that industrialized countries will keep cutting their carbon dioxide output.

The G-77 has played a significant role in shaping the debate here. But as the conference moves closer to a deal, serious fissures have erupted inside this group.

The oil-producing countries of Saudi Arabia, Venezuela and Sudan have pressed for some kind of compensation if a global crackdown on carbon puts a crimp on their exports. China, trying to hold onto its "developing" status despite its rise as a global power, has opposed the idea of incorporating its voluntary climate targets in an international agreement.

And Bolivian President Evo Morales told delegates in Copenhagen on Wednesday that rich countries should pay climate "reparations" and that the world should try to limit warming to less than the 3.6-degree rise that other leaders have agreed to.

"End the slavery of Mother Earth," Morales said at a news conference. "She's now the slave of capitalist countries."