WASHINGTON – Senator Lieberman, Independent of Connecticut, rushed to the defense today of General David Petraeus, who was branded a traitor by anti-war critics hours before telling Congress the American military needs more time in Iraq.

“The personal attack on General David Petraeus launched today by Moveon.org is an outrageous and despicable act of slander that every member of the Congress — Democrat and Republican — has a solemn responsibility to condemn,” Mr. Lieberman said in a statement.

MoveOn.org, a grassroots anti-war group, took out a full-page ad in today’s the New York Times to accused General Petraeus, the top American military commander in Iraq, of “cooking the books” on the war for the White House. “General Petraeus or General Betray Us?” the ad said.

Mr. Lieberman said General Petraeus has served his country for more than 35 years, risking his life in combat and serving lengthy military deployments away from his family, Mr. Lieberman said.

“For this, he deserves the respect, admiration, and gratitude of every American — not the disgraceful slander of MoveOn.org,” the senator said.

MoveOn.org dismissed Mr. Lieberman’s comments.

“We stand by our ad — every major independent study and many major news organizations cast serious doubt on Petraeus’ claims,” an executive director of MoveOn.org Political Action Committee, Eli Pariser, said in a statement.

General Petraeus and Ambassador Ryan Crocker appeared today in the first of three hearings on Capitol Hill this week. Lawmakers are focusing on the future course of the unpopular war, which in four years has claimed the lives of more than 3,700 American troops.

The hearings are expected to set the stage for renewed debate in Congress on bringing home American troops.

Mr. Lieberman has been among the war’s strongest defenders in Congress. He warned that congressional attempts to legislate troop withdrawals would undercut “significant” security gains the military has made in Iraq.

Anti-war Democrats, dismissing Bush administration assertions that seven months of troop increases might be working, plan to press for target dates to bring American soldiers home.

Mr. Lieberman said he did not expect those efforts in Congress to succeed, despite the unpopularity of the war.

“As unhappy as a majority of Americans probably are with Iraq, they don’t want to lose it to Al Qaeda and Iran,” Mr. Lieberman said.

Mr. Lieberman and Senator McCain, Republican of Arizona, said in an op-ed piece in today’s Wall Street Journal that American commanders, not politicians, should set any timelines for troop withdrawals.

“As al-Qaida in Iraq continues to be hunted down and rooted out, and the Iraqi Army continues to improve, the U.S. footprint will no doubt adjust,” the senators wrote. “But these adjustments should be left to the discretion of Gen. Petraeus, not forced on our troops by politicians in Washington with a 6,000-mile congressional screwdriver, and, perhaps, an eye on the 2008 election.”

Mr. Lieberman opposes a compromise plan floated by some Democrats that would set a date for beginning troop withdrawals, but would not impose a deadline for completing the pullout.

Mr. Lieberman said America could expect to have some troops there for a number of years, but he hopes the numbers can start decreasing next year as Iraqi security forces improve.

“I’d like to see the number of troops there go down — hopefully next year in response to the increasing ability of the Iraqi military,” he said.