In long-awaited testimony, the commanding general of the war said last winter's buildup in U.S. troops had met its military objectives "in large measure."
As a result, he told a congressional hearing and a nationwide television audience, "I believe that we will be able to reduce our forces to the pre-surge level ... by next summer without jeopardizing the security gains we have fought so hard to achieve."
Petraeus unleashed a volley of numbers to support his claim the surge is working, reports CBS News national security correspondent David Martin. He said the number of attacks in Iraq is lower than at any time in more than a year; civilian deaths are down by 45 percent; and sectarian killings are down by 55 percent.
But the charts show violence is still high, running at levels comparable to 2005, before the bombing of the Samarra mosque triggered sectarian fighting that nearly tore Iraq apart, adds Martin.
Testifying in a military uniform bearing four general's stars and a chestful of medals, Petraeus said he had already provided his views to the military chain of command.
Rebutting charges that he was merely doing the White House's bidding, he said firmly, "I wrote this testimony myself. It has not been cleared by nor shared with anyone in the Pentagon, the White House or the Congress."
Petraeus' testimony came at a pivotal moment in the war, with the Democratic-controlled Congress pressing for troop withdrawals and the Bush administration hoping to prevent wholesale Republican defections.
Ambassador Ryan Crocker, testifying alongside Petraeus, strongly suggested the administration's troop buildup had prevented a debacle.
Crocker said 2006 was a "bad year for Iraq. The country came close to unraveling politically, economically and in security terms. 2007 has brought improvement."
But Crocker, evaluating Iraq's ability to govern itself, the ultimate goal of the surge, has a lot fewer success stories to point to than Petreaus, reports CBS News chief White House correspondent Jim Axelrod, with a paralyzed parliament unable so far to pass major laws that would foster Sunni-Shiite reconciliation.
"I do believe that Iraq's leaders have the will to tackle the countries pressing problems, although it will take longer than we originally anticipated," said Crocker.
Mr. Bush and his political allies have worked forcefully in recent weeks to shore up Republican support. One organization with ties to the administration has spent millions on television advertisements, and Mr. Bush traveled to Anbar province last week to highlight improved security in the vast western stretches of Iraq.
Mr. Bush also called Iraqi Prime Minister Nouri al-Maliki in the hours before Petraeus spoke, and is expected to deliver a nationwide address on the war in the next few days.
Mr. Bush has urged lawmakers to listen to Petraeus with an open mind, but CBS News correspondent Chip Reid reports many influential Democrats said they already know what he's going to say and have already rejected it.
"The president's policy as well as his surge are not working," Sen. Joe Biden, D-Del., told CBS News. "The policy was to build up the Iraqi army so we could stand down. It's an abject failure."
Petraeus said that a unit of about 2,000 Marines will depart Iraq later this month, beginning a drawdown that would be followed in mid-December with the departure of an Army brigade numbering 3,500 to 4,000 soldiers.
After that, another four brigades would be withdrawn by July 2008, he said. That would leave the United States with about 130,000 troops in Iraq, roughly the number stationed there last winter when President Bush decided to dispatch additional forces.
He said he believes withdrawals could continue even after the 30,000 extra troops go home, but added that it would be premature to make any further recommendations.
Initial reaction from Democrats was sour.
Rep. Tom Lantos, D-Calif., chairman of the House Foreign Affairs Committee, said it was a "token withdrawal," and Petraeus rebutted him swiftly.
"A very substantial withdrawal," he countered.
The extent of any improvement in Iraq has been a matter of debate. The Government Accountability Office, a congressional agency, recently reported that Iraq has partially achieved only four of 18 political and military goals.
An administration report earlier this summer showed mixed results, as well.
While Petraeus focused his remarks mostly on military matters, he also noted the failure thus far of the Iraqi government to take the actions needed to stabilize the country for the long term.
"Lack of adequate governmental capacity, lingering sectarian mistrust, and various forms of corruption add to Iraq's challenges," he said.
Using 13 pages of colorful charts, Petraeus conceded that the military gains have been uneven in the months since Bush ordered the buildup last winter.