WASHINGTON — Former CIA Director David Petraeus, the architect of the US troop surge in Iraq in 2007, told lawmakers Tuesday that Syria has become a "geopolitical Chernobyl" of extremism and chaos, and called for the US to act more aggressively against the regime of Syrian President Bashar al-Assad and its air power.

"Like a nuclear disaster, the fallout from the meltdown of Syria threatens to be with us for decades, and the longer it is permitted to continue, the more severe the damage will be," Petraeus testified before the Senate Armed Services Committee. The retired four-star general once commanded military operations in Afghanistan and Iraq.

Petraeus opened with an apology to the committee and the American people in what was his first congressional appearance since pleading guilty to leaking classified information to his mistress and biographer, Paula Broadwell. In April, he was sentenced in federal court to two years probation and a $100,000 fine, and this was his first public testimony since.

"Four years ago, I made a serious mistake — one that brought discredit on me and pain to those closest to me," he said. "It was a violation of trust in me and a breach of the values to which I had been committed my whole life."

Lawmakers were complimentary of Petraeus, particularly committee Chairman Sen. John McCain, R-Ariz., who called Petraeus "one of our most distinguished leaders" and credited Petraeus' testimony in 2007 as influencing the approval of the surge.

Sen. Jeff Sessions, R-Ala., said his respect for Petraeus was "unmatched," and Sen. Angus King, I-Maine, lauded the apology as an indication of Petraeus' character.

Asked after the hearing why he had apologized when he had done so before, Petraeus said, "I thought I owed this body."

Focusing on Iraq, Syria and Iran, Petraeus cast the post-Arab Spring upheaval in the Middle East as having dire ramifications for the US, where the Sunni Islamic State and Shiite Iran seek primacy in a new regional order. The testimony provided ammunition for representatives lawmakers from both sides of the aisle who at varying levels feel the US should be doing more, particularly against the Islamic State.

"International peace and security do not require the United States to solve every crisis, to intervene in every conflict," he said. "But if America is ineffective or absent in the face of egregious violations of the most basic principles of the international order that we have championed, our commitment to that basic order is inevitably questioned, and further challenges to it are invited."

On Syria, Petraeus said the US needs to take more aggressive action against the Assad regime and its Air Force. The US, he said, should commit to protecting Sunni Arabs fighting the Islamic State against all enemies and halt Assad's Air Force from dropping barrel bombs, a leading cause of civilian casualties, radicalization and the refugee crisis in Syria.

Petraeus recommended that the US tell Assad to halt use of barrel bombs or the US will stop the Syrian Air Force from flying. He supports the establishment of enclaves protected by coalition airpower for refugees and moderate Syrian forces. Such forces would have a "constellation" of US assets overhead, radios to call for support and perhaps US forces with them.

"Our military can figure out how to keep Assad's Air Force from flying," Petraeus said.

King asked whether the US should arm the Syrian rebels rather than escalate to a US-involved air war. Petraeus said the fear would be that the weapons could wind up in the wrong hands and be used to down civilian aircraft.

Sen. Jeanne Shaheen, D-N.H., asked Petraeus whether the US should abandon its train-and-equip program for Syrian fighters, given the revelation last week that it had only four or five trained fighters on the battlefield. Petraeus said no.

"You can't abandon it because anything we want to accomplish in Syria has to be accomplished by a force on the ground," Petraeus said. "We have to pledge to support them against anybody who comes after them."

Petraeus cautioned not to hurry to oust Assad without understanding what will follow. Assad, because he is responsible for the displacement and deaths of his own people, and acts as "the magnetic attraction bringing jihadis to Syria," to fight his regime, he said.  

Overlapping with McCain's positions, Petraeus said that without US initiative, Russia and others will step in. Petraeus' assessment was that Russian President Vladimir Putin wants to resurrect the Russian empire and was seeking to revive Russian relationships in the Mideast, in part to secure its sole Mediterranean naval base in Tartus, Syria.

"Russia is an important power," Petraeus said. "It has been provocative. We don't need to be provocative in return, but we do need to be firm in return."

On Iraq, Petraeus saw a need for a greater commitment of personnel, saying the US should embed adviser elements at Iraqi brigade headquarters for forces fighting the Islamic State. He said it is worth exploring the use of joint tactical air controllers, a move the administration has been reluctant to make but is championed by its Republican critics.

"That said, we should exercise restraint to ensure our forces not take over Iraqi units," he said. "I would not embed US personnel at the Iraqi battalion level, nor would I support clearance operations before a viable hold force is available."

Sen. Lindsey Graham, R-S.C., and a 2016 presidential contender, asked whether Petraeus favored increasing troop presence. Petraeus replied he favors having more advisers, not ground forces at a tactical level.

Iraqi Prime Minister Haider al-Abadi's reform and inclusion efforts, Petraeus said, would be the key to building a sustainable government and successful Iraqi fighting force — which the US must support through coordinated diplomatic and military efforts.

After the Iran nuclear agreement, which Petraeus said he understood as providing near-term stability, the US must make clear it will meet an Iranian move toward enriching uranium with military force. He called on the administration and Congress together to make an "ironclad" declaration to that effect.

The US must work with Arab and Israeli partners to counter Iran's malign activities — including expedited approval of weapon systems sought by partners in the Mideast and a greater integration of their capabilities. Petraeus echoed the call by Defense Secretary Ash Carter for the gulf states to integrate their ballistic missile defense capabilities.

"We have to be careful because there's an insatiable desire — the requests never stop," Petraeus said of weapon sale requests, "but we should reassure our allies."

Twitter: @reporterjoe