In a return to the foreign policy stage, former CIA director tells Senate panel that US must offer protection to Syrian fighters in order to team up against Isis

David Petraeus, the former commander of the US war in Iraq, urged Barack Obama to credibly threaten Bashar al-Assad’s air force as a way through the bloody morass in Syria on Tuesday.

In a formal return to the Washington foreign policy stage, Petraeus, the retired army general who led the US occupation of Iraq through its greatest period of tactical success, told a Senate panel that the US would not be able to persuade Syrian fighters to work with it against Isis unless it offered them protection against Assad’s air-launched barrel bombs.

“If the barrel bombs continue, then the air force goes down,” Petraeus told the Senate armed services committee on Tuesday.

Petraeus, Obama’s second director of the Central Intelligence Agency, had joined with Hillary Rodham Clinton, the former secretary of state and current Democratic presidential candidate, in advising Obama to aggressively arm Syrian rebels in 2012.

Obama was unpersuaded, but in 2014 authorized the Pentagon to do so after the rise of Isis, a plan that yielded only “four or five” active fighters, the general in charge of Central Command – the US military command in charge of forces in the Middle East and South Asia – testified on 16 September. Central Command, attempting to stanch the damage from a bruising testimony, announced 70 more late on Monday.

Petraeus called Syria a “geopolitical Chernobyl” in open-ended testimony on Middle East policy and said it was conceivable that the country, besieged by four years of multifaceted war, would permanently fracture.

He argued – in contradiction to the views of Central Command chief Lloyd Austin – that the US military ought to patrol a corridor by air to create a safe zone for Syrian civilians, partly as a staging ground for a Syrian opposition to fight both Assad and Isis, one that includes Syrians who do not take part in the shaky US initiative to train and equip so-called “moderate” fighters.

“Pushing everybody through that is not necessarily the solution for ramping up,” Petraeus said.

Petraeus did not suggest significant alterations to the US mission in Iraq, principally calling for US forces on the ground to spot for airstrikes and questioning whether the rules under which pilots can fire on targets were “too restrictive”. He called the overall war against Isis a “fairly dynamic stalemate”.

Petraeus, who followed his Iraq generalship by helming Central Command and then the Afghanistan war, also offered a mixed and qualified assessment on the Iran nuclear deal. He praised its provisions to end Iranian pathways to a plutonium weapon and to “snap back” sanctions in the event of Iranian violation. His worry, he said, stretched beyond the agreement, to Iranian cash infusions to a foreign policy that could destabilize the region.

“What will be the relationship of the United States to Iranian power? Will we seek to counter it or accommodate it?” Petraeus asked.

The subtext of Petraeus’s testimony was his long-desired return to public life after a disgrace. A sex scandal with his biographer compelled the retired general to step down as CIA director in 2012, a reversal as steep as Petraeus’s ascent in 2007 as commander of the Iraq war, and was compounded by his guilty plea in March to passing classified information to the woman he had the affair with, Paula Broadwell, a married US army reserve officer who met Petraeus while researching a book about his wartime leadership in Iraq and Afghanistan.

In an attempt to draw a line under his fall from grace, Petraeus offered the committee a public apology for the affair.

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

“There is nothing I can do to undo what I did. I can only say again how sorry I am to those I let down and then strive to go forward with a greater sense of humility and purpose, and with gratitude to those who stood with me during a very difficult chapter in my life.”

Petraeus has spent much of his exile planning to make it as brief as possible. He has offered quiet advice to the Obama White House about the war against the Islamic State, begun to resurface for interviews, and lent his name to open letters on policy, a traditional marker of status in foreign affairs.

Though most often embraced by conservatives like Senator John McCain, chairman of the Senate armed services committee – and Patraeus pointedly implied on Tuesday that he had briefed the Senate panel behind closed doors – Petraeus has high praise for Clinton, with whom he often found himself aligned within the Obama administration.

It has not been a seamless return. Most recently, Petraeus offered a widely mocked proposal for working alongside “moderate” members of al-Qaida against Isis, presenting the idea as a 2015 version of the 2006-07 Anbar Awakening, in which Sunni tribesmen turned against al-Qaida in Iraq. Petraeus told the Senate panel on Tuesday that call had been misunderstood.