Jan 30 (Reuters) - Republican presidential front-runner John McCain and his chief rival Mitt Romney clashed over Iraq and their conservative credentials during a debate on Wednesday in California at the Ronald Reagan Presidential Library.

The candidates also faced questions on economic stimulus, immigration and other issues.

Here are some quotes.

MITT ROMNEY, FORMER MASSACHUSETTS GOVERNOR:

"I do not propose nor have I ever proposed a public or secret date for withdrawal (from Iraq). It's just simply wrong."

"Raising it a few days before the Florida primary when there was little time for me to try to correct the record, when the question most frequently asked is 'Oh, you're for a specific date of withdrawal?' sort of falls in the kind of dirty tricks that I think Ronald Reagan would have found to be reprehensible."

"If you get endorsed by The New York Times, you're probably not a conservative." (McCain was endorsed by the Times)

JOHN MCCAIN, ARIZONA SENATOR:

"I am proud of my record, and I am proud of reaching across the aisle and getting things done. That's what the American people want us to do."

"I think my friend Gov. Huckabee, sir, will attest to the millions of dollars of attack ads and negative ads you (Romney) leveled against him in Iowa, the millions of dollars of attack ads you have attacked against me in New Hampshire, and have ever since. A lot of it is your own money. You're free to do with it what you want to. You can spend it all. But the fact is that... ... your negative ads, my friend, have set the tone, unfortunately, in this campaign."

"We have an obligation to try to stem these greenhouse gas emissions. And one of the ways is through the use of nuclear power. The French generate 80 percent of their electricity with nuclear power. I think that -- by the way, we now have a pro-American president in France, which shows if you live long enough, anything is possible in this world."

MIKE HUCKABEE, FORMER ARKANSAS GOVERNOR:

"I think what Americans are looking for is somebody to just be honest with them and straight with them and tell them that, no, it's not better and it's not going to get better unless we have some serious leadership in Washington that says that we're going to have to start having policies that touch the people not just at the top, but the people at the bottom.

"If we end up with the (tax) rebates, we're going to borrow the $150 billion from China. And when we turn it into rebates, most people are going to go out and buy some consumables like a pair of shoes that they probably don't even need, but they're going to buy them, and they're most likely an import from China. My point is, whose economy are we stimulating when we do that?"

RON PAUL, TEXAS CONGRESSMAN:

"It's (Iraq) an undeclared war. And we have these silly arguments going on about who said what when. I think it's time to debate foreign policy and why we don't follow the Constitution and only go to war with a declaration of war."

"No, no, we're not better off. We're worse off, but it's partially this administration's fault and it's the Congress. But it also involves an economic system that we've had for a long time and a monetary system that we've had and a foreign policy that's coming to an end and we have to admit this." (Compiled by JoAnne Allen; Editing by Patricia Zengerle)