(Adds Giuliani comment, paragraph 12-13)

By Claudia Parsons

NEW YORK, Sept 13 (Reuters) - An ad criticizing the top U.S. general in Iraq raised charges on Thursday that The New York Times <NYT.N> slashed its advertising rates for political reasons -- an accusation denied by the paper.

The ad by liberal anti-war group moveon.org ran on Monday, the day of Gen. David Petraeus' testimony to Congress about the war and how long U.S. forces will stay in Iraq.

Moveon.org confirmed it paid $65,000 for the full page ad headlined "General Petraeus or General Betray Us."

The New York Post ran a story on Thursday asking why the basic rate of $181,692 for such an ad was discounted.

"Times Gives Lefties a Hefty Discount for 'Betray Us' Ad," was the headline in the Post, owned by Rupert Murdoch's News Corp. <NWSa.N>.

Times spokeswoman Catherine Mathis denied the rate charged indicated a political bias and said it was the paper's policy not to disclose the rate paid by any advertiser.

"We do not distinguish the advertising rates based on the political content of the ad," Mathis told Reuters.

"The advertising folks did not see the content of the ad before the rate was quoted," she said, adding that there were over 30 different categories of ads with varying rates.

Mathis confirmed the open rate for an ad of that size and type was around $181,000. Among reasons for lower rates are advertisers buying in bulk or taking a standby rate, she said.

"There are many instances when we have published opinion advertisements that run counter to the stance we take on our own editorial pages," she said.

'COOKING THE BOOKS'

The ad in the main news section of the Times accused Petraeus of "cooking the books for the White House."

Rudy Giuliani, a leading candidate for the Republican presidential nomination, criticized the Times over the ad which he called a "character assassination" of Petraeus.

"(I) call upon The New York Times to give us the same rate, the heavily discounted rate they gave moveon.org for that abominable ad," the former New York mayor told reporters in Atlanta, adding he would be seeking to place an ad on Friday.

The ad angered Republicans, including Rep. Duncan Hunter of California, a presidential candidate who brought it to the Petraeus hearing on Monday and waved the ad in the air, telling lawmakers he was "irritated" by it.

Jeff Jarvis, a journalism professor who blogs on media at buzzmachine.com, said the key question for the Times was could any other political or advocacy group get the same rate under the same circumstances.

"The quandary the Times gets stuck in is they don't want to admit you can buy an ad for that rate, no matter who you are," Jarvis said, noting that with print advertising revenues in decline newspapers generally did offer big discounts.

On a more general note, Jarvis said U.S. papers should emulate their counterparts in Britain where, for example, The Guardian makes no effort to hide its liberal stance.

"In the U.S., I would argue newspapers should be more transparent and open about the views taken ... and the (New York) Times is liberal," he said.

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