SAN FRANCISCO – In the past ten months, Yahoo CEO Jerry Yang has faced a hostile takeover attempt by Microsoft, shareholder lawsuits, a proxy fight led by Carl Icahn and, on Wednesday, watched a much-needed partnership with Google (GOOG) go up in flames.  Yet the embattled Yahoo chief says he has no regrets that he took on the job.

“I didn’t make the decision of being the CEO lightly,” Yang told a packed crowd of 800 at the Web 2.0 Summit late Wednesday afternoon, hours after Google announced it was pulling out of an ad partnership with Yahoo to avoid a federal antitrust suit.

“I wanted to make a change at Yahoo that I believe I can make,” he said. “That’s a dream that I felt I could achieve by being CEO, and that’s still the dream today. And that’s something that gets lost underneath all these external issues.”

He added, “I don’t regret any minute of it. It might not be the most fun thing, but I feel like I only know how to operate by caring and being passionate about Yahoo.  I just feel that’s the reason that I’m here.”

Yang appeared relaxed while facing tough questions from Web 2.0 impresario John Battelle, who conducted the 45-minute interview at San Francisco’s Palace Hotel. Dressed in a purple-checkered dress shirt, Yang smiled and joked with Battelle who asked him to justify his job and why he rejected Microsoft’s offer to buy the company.

“What happened?” Battelle asked.

“Which part?” Yang said with a smile.

“Thirty-three dollars a share, Jerry. What happened?”

Since Microsoft (MSFT) and Yahoo (YHOO) ended talks in June, Yang has said that the company was willing to sell to Microsoft for the right price. He reiterated his position that he’s still willing to sell the entire company or Yahoo’s search business at the Web 2.0 Summit.

Not convinced, Battelle blamed Yang for failing to get the deal done. “You didn’t want it to happen,” Battelle said.

“I don’t have an ego,” Yang replied. “At the end of the day, we believed the deal was going to be done, and that a deal was not that far apart and they walked away…I know [the failure of the deal] is something that I’ll be labeled with.”

It was the failure of that other deal that seemed to stun Yang. After four months of negotiating with the feds, Google on Wednesday pulled out of a search ad deal that would have generated hundreds of millions of dollars in additional cash flow for Yahoo.

Yang mentioned several times that he was “disappointed” by Google’s decision. “We were working with the Department of Justice to get this deal done,” he said. “We also felt that Google clearly did not want to stay in the deal, and we were disappointed with that.”

Yang had no answer for why Google withdrew. He said, “You’d have to ask them because we are certainly disappointed.”

In a blog post, Google’s chief legal officer David Drummond referred to the deal as too “risky.” The feds threatened to sue Google and Yahoo if they went through with the ad agreement that would allow Yahoo to run some Google search ads on Yahoo’s web properties. The Justice Department believed combining the No. 1 and No. 2 search engines was anticompetitive. Yahoo signaled it was willing to go to court over the deal.

Said Yang, “I really thought the government in this case does not understand this industry. Their thinking is too narrow. I clearly don’t agree with their point of view.”

Yang stressed that the company had “no news” with regards to reviving talks with Microsoft. He also stayed mum on reported talks to buy AOL, which is owned by Fortune’s parent company Time Warner (TWX).

“Are you buying AOL,” Battelle pressed.

Yang laughed and then smiled. “I can’t talk about that. If I tell you, I’d have to kill you.”

Said Battelle, “I think I’ll take the bullet for this audience.”