RICHARDSON, Texas -- Maybe all the criticism from Rush Limbaugh is sinking in.

Republican presidential hopeful Sen. John McCain almost called himself a liberal on Thursday, getting ahead of himself as he contrasted himself with the Democratic candidates.

"I'm a proud, conservative, liberal Republi- Hello! Easy there," McCain said, laughing along with his audience at Texas Instruments Inc.

He corrected himself immediately. "Let me say this: I am a proud, conservative Republican, and both of my possible or likely opponents today are liberal Democrats."

A "liberal" label is sometimes applied to McCain by conservative foes such as Limbaugh who dislike some of his moderate stances and his willingness to work with Democrats. Still, the Arizona senator has made inroads with many critics since becoming the GOP nominee-in-waiting.

McCain was answering a question about whether he would aggressively campaign against Democratic Sens. Barack Obama or Hillary Rodham Clinton.

"Yessir, I will, but I also want to say, I think Americans are a little bit tired of all these negative ads," McCain said. "I want to assure you that I have in this primary, and in my past election campaigns, and in this one, I will conduct a respectful debate."

Then he made one more slip: "Now, it'll be dispirited -- it'll be spirited, because there are stark differences," McCain said.

He concluded: "So there will be strong differences of views and policies in the future of America."