WASHINGTON — General David Petraeus, opening a historic appearance by a wartime theater commander before Congress, is being greeted by Democrats who are straddling the fence between deference and disbelief.

The chairman of the House Foreign Affairs Committee, Tom Lantos, yesterday captured the balancing act in his opening remarks at the House hearing where General Petraeus gave his assessment of the military surge in Iraq that began its operational phase at the end of June. In remarks that began with praise for the general and Ambassador Ryan Crocker as two of America’s most “capable public servants,” the California Democrat soon changed gears.

“This is not a knock on you, General Petraeus, or on you, Ambassador Crocker. But the fact remains, gentlemen, that the administration has sent you here today to convince the members of these two committees and the Congress that victory is at hand,” Mr. Lantos said. “With all due respect to you, I must say … I don’t buy it.”

Neither did one of the biggest donors to the Democratic Party, MoveOn.org, which took out a full-page advertisement in yesterday’s New York Times calling General Petraeus “General Betray-us.” The ad became one of the major themes of the nearly six-hour hearing that kicked off General Petraeus’s and Mr. Crocker’s visit to Washington from Baghdad. Indeed, before the general got to the meat of his presentation, he stipulated that his words were his own and not, as Democrats had been saying for the past week, the “Bush report.”

“At the outset, I would like to note that this is my testimony. Although I have briefed my assessment and recommendations to my chain of command, I wrote this testimony myself. It has not been cleared by, nor shared with, anyone in the Pentagon, the White House, or Congress,” General Petraeus said.

Ranking Republicans on both the House Foreign Affairs and House Armed Services committees at various points asked their Democratic colleagues to distance themselves from the MoveOn.org advertisement. The Democratic leaders, Mr. Lantos and Rep. Ike Skelton of Missouri, however, did not budge.

Nor did many other leading Democrats, although Senator Kerry of Massachusetts, the party’s nominee in 2004 who withdrew his bid for the nomination in 2008 to devote his time to ending the war in Iraq, said yesterday on CNN that he thought the advertisement was “over the top.”

When asked for a response, a spokeswoman for Senator Obama of Illinois, Jennifer Psaki, tried to distance the Democratic presidential candidate from the ad. “Senator Obama’s question is not about General Petraeus’s patriotism. It’s about his logic,” she said. “There’s no evidence that this surge is producing the political progress needed to resolve the civil war in Iraq, or that it will be accomplished through more of the same.”

Senator Clinton, the New York Democrat who is Mr. Obama’s chief rival for the presidential nomination, did not speak to the MoveOn.org advertisement head on. When asked about the ad, a spokesman for her campaign, Blake Zeff, accused Republicans of using a diversionary tactic. “It is unfortunate that Republican presidential candidates are focused on generating a political sideshow instead of discussing the president’s failed war policy,” Mr. Zeff said. “Senator Clinton is going to keep her focus where it should be, on ending the war.”

The executive director of the MoveOn.org political action committee, Eli Pariser, challenged Republicans to point out any errors in the ad. “We stand by our ad,” he said in a statement. “Every major independent study and many major news organizations cast serious doubt on Petraeus’s claims.”

In response to the ad, the House minority leader, John Boehner of Ohio, introduced a resolution praising General Petraeus’s integrity and chastising MoveOn.org.

The hearing itself brought few surprises. General Petraeus pointed to progress he saw in the security sector, while Mr. Crocker voiced less optimism about the prospect of a quick political accord. Because of the improvement in security, particularly in places such as Anbar province, General Petraeus said he was recommending that some five brigades be withdrawn from the battlefield by next summer, as long as Iraqi security progresses at its current rate.

“The progress our forces have achieved with our Iraqi counterparts has, as I noted at the outset, been substantial,” General Petraeus said. “While there have been setbacks as well as successes and tough losses along the way, overall our tactical commanders and I see improvements in the security environment.”

Mr. Crocker emphasized the problems that could arise from any precipitous withdrawal of soldiers that is not linked to the level of security, noting that President Ahmadinejad of Iran has already warned that his country will fill the void when the Americans leave.

“Our current course is hard,” Mr. Crocker said. “The alternatives are far worse.” He did say, however: “A secure democratic Iraq at peace with its neighbors is attainable.”

“There will be no single moment,” he added. “Any turning point will only be recognized in retrospect.”

Prime Minister al-Maliki saw his government nearly collapse in August after a coalition of fundamentalist Sunni Islamic parties withdrew from the government, followed by the secular parties. Yesterday, Mr. Maliki gave an address to parliament boasting that Iraq would avoid a civil war.

In response to a question about Al Qaeda, Mr. Crocker spoke of how the terrorist network’s “Taliban-like rule” in Anbar resulted in children being beheaded and cigarette smokers having their fingers cut off.

The ambassador — who was a lead negotiator with Iran in 2001 and 2002 in an Afghanistan reconstruction conference in Bonn, Germany, which through a United Nations grouping included Afghanistan, its neighbors, and America and Russia — said he was not hopeful about the current negotiating track with the Iranians.

In response to questions from Mr. Lantos, Mr. Crocker said: “I found a completely different atmosphere than that I experienced in 2001 and 2002. … I laid out activity damaging to Iraqi security, and there was no readiness of Iran at all to engage seriously on these issues.”

Mr. Crocker has met three times with the Iranian ambassador, Hassan Kazemi Qomi, in Baghdad and has not come away from those meetings with glowing reviews. But his assessment yesterday was the most pessimistic to date and comes just four weeks before a foreign minister-level meeting of America, Iraq, and its neighbors. Mr. Crocker said he has not seen any movement from the Iranians to address their role in working with anti-government forces in Iraq.

General Petraeus also emphasized the spoiler role Iran was playing in Iraq, pointing to the capture of the deputy commander of the Tehran-sponsored Hezbollah Unit 2800, a special force that works with Iran’s Quds Force to assist elements of the Shiite Mahdi Army. “These elements have assassinated and kidnapped Iraqi governmental leaders, killed and wounded our soldiers with advanced explosive devices provided by Iran, and indiscriminately rocketed civilians in the International Zone and elsewhere,” the general said. “It is increasingly apparent to both coalition and Iraqi leaders that Iran, through the use of the Quds Force, seeks to turn the Iraqi special groups into a Hezbollah-like force to serve its interests and fight a proxy war against the Iraqi state and coalition forces in Iraq.”

[In other Iraq-related news, the American military reported the deaths of nine soldiers yesterday — including seven killed in a vehicle accident — according to the Associated Press.

In western Baghdad, seven American soldiers were killed in a vehicle accident that also claimed the lives of two detainees, the military said. Eleven soldiers from Multinational Division-Baghdad and one detainee were also injured in the west Baghdad accident, the military said without giving further details. Another American soldier was killed and two were injured when their vehicle overturned east of the capital, the military said in a statement. The military also said a soldier died Sunday of wounds suffered in fighting near Kirkuk.]