UPDATE 2-US pledges "ambitious actions" in UN climate pact

* U.S. promises "ambitions actions" in climate pact

* Urges "dramatic increase" in aid to developing nations

* Rich nations should set goals for 2020 and 2050 (Adds details, quotes)

By Alister Doyle, Environment Correspondent

OSLO, May 5 (Reuters) - The United States promised on Tuesday to take "ambitious actions" under a new U.N. pact to fight global warming and urged a dramatic increase in cash to help developing nations cope with climate change.

A submission to the United Nations outlining Washington's ideas for a treaty due to be agreed in Copenhagen in December also said many nations should outline greenhouse gas cuts both for a mid-term goal of 2020 and a long-term 2050 target.

"The United States is committed to reaching a strong international agreement in Copenhagen based on both the robust targets and ambitious actions that will be embodied in U.S. domestic law," it said.

It added that the U.S. pledge hinged on "important national actions of all countries with significant emissions profiles to contain their respective emissions."

China has recently overtaken the United States as the top emitter, ahead of Russia and India. But China's per capita emissions, mostly from burning fossil fuels, are less than a quarter of those of the United States.

President Barack Obama plans to cut U.S. emissions back to 1990 levels by 2020, a reduction of about 14 percent from 2007 emissions. The U.N. Climate Panel says rising world emissions will cause more floods, heatwaves, droughts and rising seas.

"The U.S. is keenly aware of the need for a dramatic increase in the flow of resources available to developing countries ... to address the climate challenge," the submission said.

FLOODS, DROUGHTS

Cash was needed both to help developing nations curb their emissions and to adapt to a changing climate, for instance by building flood defences or developing drought-resistant crops.

"Resources will need to flow from a wide variety of sources, including, for example, public sources in developed and developing countries, private investment, and - in the case of mitigation - the carbon market," it said.'

It did not estimate how much cash was needed nor say whether new funding mechanisms were needed. African nations said last month that developing countries would need $267 billion a year by 2020 to cope with climate change.

The U.N. Climate Panel has said rich nations need to cut emissions by between 25 and 40 percent below 1990 levels by 2020 to avert the worst of climate change. Poor nations' emissions should show a "substantial deviation" below projected growth.'

The U.S. submission did not suggest targets for cuts but called for developed nations to set goals for reductions both for 2020 and beyond to mid-century. Washington wanted commitments to be legally binding, it said.

"Parties shall formulate and submit low-carbon strategies that articulate an emissions pathway to 2050," it said. Less poor developing nations should also join in setting goals.

Washington also gave backing to planned measures to give developing nations credits for preserving forests -- trees soak up carbon dioxide as they grow.

The submission, published on the website of the U.N. Climate Change Secretariat, was made after an April 24 deadline that has also been overshot by many countries. The United States would add more ideas at a later date.

The next round of U.N. negotiations is in Bonn from June 1-12. For details of the submission, the U.N. website is: here

-- For Reuters latest environment blogs click on: blogs.reuters.com/environment/ (Editing by Jon Hemming)