WASHINGTON — Sen. Richard Lugar said today that he doesn’t know how a bill to limit greenhouse gas emissions could be crafted to win his support, despite his strong interest in climate change.

In speeches delivered in Indiana and Washington this week, the Indiana Republican talked about the international crises that could result from droughts, food shortages, rising seas and other consequences of global warming.

“I believe that the U.S. must attempt to reduce greenhouse gas emissions,” Lugar said Monday during a speech in Indianapolis on energy security and climate change.

But Lugar opposes a bill passed by the House that would limit greenhouse gas emissions through a cap-and-trade system in which polluters could buy credits from non-polluters.

He said the bill’s problems include provisions that would give too many benefits to non-coal-dependent states to help in the transition away from fossil-fuels and not enough to coal-dependent states like Indiana.

“To give the impression that somehow the Senate must pass a bill comparable to the House, or anything in that ballpark, seems to me is not a very good idea and is one I’m likely to oppose,” Lugar said today in a meeting with reporters before he delivered a speech on world hunger.

Asked what kind of bill he could support, Lugar answered, “I frankly don’t know, although I’m deeply interested in this.”

Lugar said there are other steps the United States can take to improve energy efficiency and promote renewable fuels.

“The real way of approaching this is through conservation, through building modification, through the change in how electricity is delivered,” Lugar said. “We can make a difference now, which seems to me to a better idea. But it has to be in a quantity that’s significant.”

The White House hopes the Senate will approve a climate change bill this fall, making it easier for the United States to argue at a December climate change summit in Copenhagen that other countries also need to do their part.

The Union of Concerned Scientists, which is pushing for action, has said the road to Copenhagen runs through the Midwest because of concerns from lawmakers like Lugar and Democratic Sen. Evan Bayh about the impact of the legislation on their coal-dependent states.

The Midwest is the world’s fourth-largest emitter of greenhouse gases behind the entire U.S., China and Russia, according to the group.

Obama told the United Nations today that “we must seize the opportunity to make Copenhagen a significant step forward in the global fight against climate change.”

But Lugar said that, even if Congress passes a climate change bill, China and India are unlikely to follow suit unless the United States and other developed nations offer financial assistance. The Chinese have suggested that the United States contribute 1 percent of its Gross National Product, Lugar said.

“That’s not only inconceivable,” Lugar said, “it’s not going to happen.”