cFormer Democratic Sen. Max Baucus of Montana focused on trade issues during the 20-minute speech before several hundred people in an upscale hotel, saying his priorities included sealing an investment treaty between the two countries.

Still, he didn't fail to bring up sensitive issues such as China's human rights record and U.S. accusations of Chinese military cyberspying.

"Cyber-enabled theft of trade secrets by state actors in China has emerged as a major threat to our economic and thus national security," the ambassador said. "We won't sit idly by when a crime is committed in the real world so why should we when it happens in cyberspace."

Baucus said "no bilateral relationship is more important than the U.S. and China's," and voiced confidence that the two countries could work closely on urgent challenges such as combatting climate change.

The two countries are the world's biggest emitters of carbon and together account for 40 percent of the world's carbon dioxide emissions, he said.

"This problem is so big and so dire that a solution is not possible without close United States-China cooperation," Baucus said. "Successful cooperation on climate change and other pressing concerns has an important byproduct: It helps our two countries build trust and better manage areas where we don't agree and where our interests are not so closely aligned."

The 72-year-old succeeds former Washington Gov. Gary Locke, who drew attention here as the first U.S. ambassador to Beijing of Chinese descent. Locke, also a former commerce secretary, had charmed some ordinary Chinese when a photograph circulated ahead of his arrival showing him buying his own coffee, appearing down to earth in contrast to Chinese officialdom.

Wednesday's speech marked a coming-out moment for Baucus, a white-haired statesman who likes to play up his roots in rugged Montana ranchland.

He reminded his audience that he had invited four Chinese ambassadors to the U.S. to visit his Montana home and had come to know many of the country's officials while serving as chairman of the Senate Finance Committee.

Still, Baucus takes on the post as China is locked in tense territorial disputes with several of its neighbors, some of which are close U.S. allies. Baucus didn't refer specifically to those conflicts but returned repeatedly to ways the U.S. and China could get past tensions and come together.

"Despite our differences, we have no choice but to keep talking and work our way through these tough challenges," he said. "It's at moments like these when more not less dialogue is needed."