The United States will offer a 17-percent reduction target of its greenhouse gas emissions below 2005 levels by 2020 at the Copenhagen Climate Summit in December, the White House said in a statement on Wednesday.

This target is about 4 percent emissions cut below 1990 levels, experts say.

The U.S. targets on emission cut also include a 30 percent reduction by 2025 and a 42 percent drop by 2030, according to the statement.

This provisional target is in line with current legislation in both chambers of Congress. The U.S. House of Representatives passed a bill in June, which sets a 17 percent reduction target for emissions by 2020 from 2005 levels. A Senate version aims for a 20 percent cut.

"The President is working closely with Congress to pass energy and climate legislation as soon as possible," the statement said.

U.N. scientists say rich countries must cut carbon emissions by 25 percent to 40 percent from 1990 levels by 2020 to prevent Earth 's temperatures from rising 2 degrees Celsius above its average temperature before the industrial era began 150 years ago. Any rise beyond that could trigger climate catastrophe, they say.

The European Union has committed to reducing its emissions of green house gases by 20 percent by 2020, compared with 1990 levels. The new government in Tokyo has pledged to reduce Japan's greenhouse gases by 25 percent by 2020, compared with 1990, if other countries make similar commitments.

The White House announced that U.S. President Barack Obama will attend the Copenhagen summit on Dec. 9. It also called on the countries of the world do what it takes to produce a strong, operational agreement in Copenhagen.

The summit is scheduled to be held from Dec. 7 to 18, where representatives of about 190 countries are expected to renew green house gases emissions reduction targets set by the Kyoto Protocol, the first stage of which is to expire in 2012. It is also expected to outline the post-2012 negotiation path.