After exhausting negotiations concluding on the eve of a global summit, UN members on Tuesday backed a plan for nursing Earth's sick environment back to health and tackling poverty through greener growth.

But relief at avoiding the nightmare of the deadlocked 2009 Copenhagen climate summit mingled with disappointment for many who thought the deal was a sad compromise.

"Nobody in that room adopting the text was happy. That's how weak it is. And they all knew," the European Union's commissioner for climate change, Connie Hedegaard, said in a tweet.

After haggling that went deep into the night, national delegates gave provisional approval to a 53-page statement designed to act as a compass for sustainable development for the next decade and beyond.

It identifies measures for tackling the planet's many environmental ills and lifting billions out of poverty through policies that nurture rather than squander natural resources.

It is expected to be endorsed by heads of state and government at the close on Friday of the 10-day Conference on Sustainable Development, the 20-year followup to the 1992 Earth Summit that is a landmark in environmentalism.

Around a hundred heads of state and government are expected to show up for the three-day meeting.

As summit host, Brazil battled to avoid asking leaders to sort out gridlocked text -- a scenario that brought the Copenhagen Summit to the brink of catastrophe.

One of the biggest areas of dispute was on "Sustainable Development Goals," or SDGs, that will replace the UN's Millennium Development Goals after these objectives expire in 2015 and on promoting the green economy.

Efforts by the European Union (EU) for text to shore up the environmental quality of the SDGs when they are negotiated in detail fell through.

Developing countries, too, failed to get any figures in paragraphs about financing sustainable growth for poorer economies. The Group of 77 and China bloc had demanded $30 billion a year.

"We have a text that has been agreed 100 percent by the 193 (UN) parties," Brazilian Foreign Minister Antonio Patriota told reporters.

"It amounts to a victory for multilateralism... after 20 years, the spirit of Rio remains alive."

German Environment Minister Peter Altmaier said he was "not 100 percent satisfied," but "after the failure of Copenhagen it is a sign of encouragement... it was very important to avoid failure at this conference."

French Development Minister Pascal Canfin sounded a similar note.

"We are not completely satisfied, but we avoided Rio+20 turning into Rio minus 20," he said.

His colleague, Ecology Minister Nicole Bricq, said there were numerous pluses in the text, and these could be improved upon in the future.

"EU pressure has helped us to jam a foot in the door and stop it from being slammed shut," Bricq said.

The US green group, the Natural Resources Defense Council, was upbeat about the deal's potential benefit for the seas but criticized it for failing to beef up environmental governance, an area of jealously-guarded national sovereignty.

"The positive steps contained in the text on plastic pollution, ocean acidification, fishing subsidies and overfishing -- if vigorously implemented - will help reverse the decline of our oceans," the director of its international program, Lisa Speer, said.

"We are exceedingly disappointed that no decision was reached to negotiate a new agreement for the conservation and management of biodiversity beyond national jurisdictions. But the acknowledged urgency for moving forward on this critical biodiversity issue is at least a step forward."

On the sidelines, 50,000 activists, business executives and policy-makers are attending the conference.

In a message to the conference, 40 figures, including former heads of state and Nobel laureates, said the scientific evidence of dangerous environmental overreach is "unequivocal."

"We are on the threshold of a future with unprecedented environmental risks," they said.

"The combined effects of climate change, resource scarcity, loss of biodiversity and ecosystem resilience at a time of increased demand poses a real threat to humanity's welfare."