Washington, D.C. ? After two weeks of denials, the New York Times acknowledged that it should not have given a discount to MoveOn.org for a full-page advertisement assailing Gen. David H. Petraeus.

The liberal advocacy group should have paid $142,000 for the ad calling the U.S. commander in Iraq “General Betray Us,” not $65,000, the paper’s public editor wrote Sunday.

Clark Hoyt said in his column that MoveOn was not entitled to the cheaper “standby” rate for advertising that can run any time over the following week because the Times did promise that the ad would run Sept. 10, the day Petraeus began his congressional testimony. “We made a mistake,” Times spokeswoman Catherine Mathis was quoted as saying.

MoveOn, saying it had no reason to believe it was paying “anything other than the normal and usual charge,” said Sunday that it would send the Times $77,000 to make up the difference.

The Times also violated its own advertising policy, which bars “attacks of a personal nature,” Hoyt reported. He wrote that the episode “gave fresh ammunition to a cottage industry that loves to bash The Times as a bastion of the ‘liberal media.'”