WASHINGTON--An influential moderate Democratic senator Tuesday warned that some carbon emission reduction targets in a climate change bill under consideration were too ambitious.

Montana Senator Max Baucus said that unless modified, these provisions would be divisive and could slow the bill's passage.

"I have serious reservations of the depth of the mid-term reduction target in the bill and the lack of preemption of Clean Act authority to regulate greenhouse gases," Baucus said during a hearing of the Senate Environment and Public Works Committee.

Baucus chairs the powerful Senate Finance Committee, which might write its own version of a climate bill.

Under the draft proposed by liberal Democratic Senators John Kerry and Barbara Boxer, U.S. utilities and companies would have to cut emissions of carbon dioxide and other gases by 20% by 2020, 42% by 2030 and 83% by 2050. Baucus appeared concerned about the 2030 target.

The legislation also would allow the U.S. Environmental Protection Agency for the first time to regulate emissions of these gases, which are blamed for global warming. A climate change bill passed by the House in June excluded EPA authority, leaving the remedy for climate change in the hands of Congress.

"We cannot afford a first step that takes us further away from an achievable consensus," Baucus said. Otherwise, he added, "we risk wasting another month, another year, another Congress without taking any steps forward for our future."

President Barack Obama and leading congressional Democrats had hoped to pass a bill to fight global warming by December, when an international summit in Copenhagen convenes to look at new goals for carbon reduction.

But increasingly, it appears that the Senate will not meet that deadline.

Baucus, who represents the coal-producing state of Montana, said he supports "common sense legislation that reduces emissions, while protecting our economy." But he also noted that agriculture and tourism in his state "cannot afford unmitigated impacts of climate change."