The United States needs to have a climate change law in place before international talks on a climate pact begin in December, two top Obama administration officials said on Monday.

The U.S. House of Representatives narrowly passed legislation in June to cut U.S. carbon emissions from utilities, manufacturers and others 17 percent below 2005 levels by 2020.

The Senate is set to take up its own version of the bill in September when lawmakers return from their summer recess.

It is unclear whether the bill will make it into law before the international climate negotiations in Copenhagen in December. The highly contentious debate over health care reform is likely to crowd the legislative agenda in the fall.

We think it is important for the president to be empowered to be able to say to the rest of the world that America stands ready to lead on this issue, Agriculture Secretary Tom Vilsack told reporters after an energy briefing at the White House.

Groups from the oil industry, agriculture and manufacturing have lined up to oppose climate change legislation, saying it would add costs for producers, farmers and consumers without guaranteeing environmental gains.

Vilsack and Commerce Secretary Gary Locke met with groups from the Midwest and Mid-Atlantic states to press their message that a climate change law would be good for the environment and economy.

A U.S. Agriculture Department study shows farmers could boost their net income by $10 billion to $20 billion in the long term earning money from offsets -- contracts to plant trees or change the way they till land to lock more carbon in soils, Vilsack said.

Locke pointed out that many developing countries such as China are resistant to fighting global warming, even though they are large emitters of greenhouse gases.

The United States needs to set a very firm and clear example if we are to be successful in getting the other countries to be equally aggressive in addressing climate change, Locke said.

Vilsack warned against delays for the climate bill.

How are we going to be able to move other nations in the same direction we want to move on trade issues or on fighting extremists if we can't deliver on climate change, when the rest of the world is moving forward? he asked.

(Additional reporting by Roberta Rampton and Christopher Doering; Editing by Lisa Shumaker)