The official said Obama, China's Premier Wen Jiabao, Indian Prime Minister Manmohan Singh and South Africa's President Jacob Zuma had reached a meaningful agreement, after a day of deep divisions between leaders of rich and developing nations.
Brazil also approved the deal that appeared to bypass other participants at UN-led climate talks in Copenhagen. The accord did not have guaranteed approval from all 193 nations. Noticeably, EU nations were absent from the meeting.
Tensions between China and the United States, the world's two biggest emitters, had been particularly acute after Obama -- in a message directed at the Chinese -- said any deal to cut emissions would be empty words on a page unless it was transparent and accountable.
Negotiators struggled all day to find a compromise acceptable to all 193 countries which could avert the threat of dangerous climate change, including floods, droughts, rising sea levels and species extinctions.
A draft text under discussion on Friday included $100 billion in climate aid annually by 2020 for poor countries to combat climate change, and targets to limit warming and halve global greenhouse gas emissions by 2050.
But it abandoned earlier ambitions for any deal in Copenhagen to be turned into a legally binding treaty next year.
Today, following a multilateral meeting between President Obama, Premier Wen, Prime Minister Singh, and President Zuma a meaningful agreement was reached, the U.S. official said.
It is not sufficient to combat the threat of climate change but it is an important first step.
No country is entirely satisfied with each element but this is a meaningful and historic step forward and a foundation from which to make further progress, the official added.
Under the five-nation agreement, rich and poor nations had agreed to a finance mechanism, emissions cuts to curb global warming to 2 degrees Celsius, and to provide information on the implementation of their actions.
Earlier, Indian environment minister Jairam Ramesh told Reuters December 7-18 meeting was close to seeing a legally non-binding Copenhagen outcome after 36 hours of grueling, intensive negotiations.
The European Union had pressed for a strong deal to limit global warming to no more than 2 degrees Celsius and which included tough carbon curbs from other industrialized nations such as the United States.
Scientists say a 2 degrees limit is the minimum to avoid some of the worst impacts of climate change including several meters sea level rise, species extinctions and crop failures.
Given where we started and the expectations for this conference, anything less than a legally binding and agreed outcome falls far short of the mark, said John Ashe, chair the Kyoto talks under the United Nations.
(With reporting by Alister Doyle, Gerard Wynn, Anna Ringstrom, John Acher, Anna Ringstrom, Richard Cowan, David Fogarty, Pete Harrison and Emma Graham-Harrison; Writing by Dominic Evans; editing by Janet McBride)