Top foreign policy advisers for the Obama and Romney campaigns laid out contrasting visions during a Wednesday debate at the Brookings Institution, dueling on issues ranging from America's role in Syria to a new era in relations with Russia.

While the presidential campaign has been dominated by economic concerns, Romney thrust foreign affairs into the spotlight with a Tuesday speech at a Veterans of Foreign Wars convention. Speaking on the eve of a trip to Israel, London and Poland, Romney offered a forceful critique of how Obama has interacted with America's adversaries and enacted cuts to the defense budget.

Romney has sought from the beginning to portray Obama as overly conciliatory and willing to concede America's military advantage, and Obama campaign press secretary Ben LaBolt derided the speech as all bluster, offering no specific plans for our relations with any region of the world. 

Michele Flournoy, co-chair of Obama's National Security Advisory Committee, and Rich Williamson, a senior foreign and defense policy adviser for the Romney campaign, fleshed out that debate on Wednesday. Here are some highlights.

Iran

Romney has said Obama's light-handed approach is enabling Iran's nuclear program. Williamson largely built on that critique, slamming a history of inconsistent messages from the administration on Iran.

There has been no credible threat of force, Williamson said. No one in Tehran or in the region believes Obama will use force.

He added that Obama bungled its reaction to Iran's Green revolution, a popular backlash against corrupt elections in 2009, with a muted response and said Romney would be more aggressive in embracing a potential military strike.

[Romney] would create a credible threat. Williamson said. He has not taken it off the table. (But neither has Obama: the president himself and top administration officials have said repeatedly that no options are off the table.)

Flournoy defended Obama's decision to initially try and engage with the Iranian regime, saying it was the only way to create international unity behind any effort to address Iran and maintaining that the effort laid the groundwork for getting Russia, China and the European Union to agree to sanctions and other measures against Iran.

She also underscored the a military strike is still possible, saying that the Pentagon planning for this is incredibly robust. It's ready.

The military option is real, Flournoy said. The president's judgment is now is not the time because there's a chance, with sanctions biting, for Iran to change its calculus.

Syria

Romney has faulted Obama for not doing more to stem the bloodshed unleashed by President Bashar al-Assad's embattled regime. The rhetoric to justify the Libya action looks pretty hollow when you look at what's happened in Syria, Williamson said.

This administration didn't send resources in to try and determine who the Syrian dissidents are and furnish them with aid, he said. He added that Romney would support arming the moderate factions within the opposition but stopped short of endorsing a plan, pushed by Sen. John McCain (R-Ariz.) to establish humanitarian safe zones using military force.

Flournoy rejected the notion that the administration has abandoned the opposition, saying they have been working with the rebels for many, many months even if press reports of the relationship have only emerged more recently. The key, she said, is to foster greater cohesion among the resistance that would allow a solution generated by Syrians, not imposed from without.

The way change will ultimately happen in Syria is if you can get parts of the inner circles around Assad to begin to defect, Flournoy said, but they need the assurance they can be part of the future Syria.

Israel

The perception that Obama has not done enough to support Israel has been a common critique of his foreign policy, bolstered by his allegedly frosty relationship with Prime Minister Benjamin Netanyahu. Flournoy rejected that characterization, noting historic levels of American aid to Israel and pointing to the United States vetoing attempts by the Palestinians to elevate their status at the United Nations.

I think there's a lot of playing politics with this issue, she said of the ostensibly strained relationship between Netanyahu and Obama.

Williamson acknowledged the level of funding but said the American-Israeli relationship has nevertheless deteriorated under Obama.

You try to get a condominium of political cooperation and that has not existed and there have been harsh differences on Iran and Israel, he said. He did not offer any details of how Romney would further a Palestinian-Israeli accord, saying there is no instant solution.

Russia

After Obama was caught on an open microphone reassuring then-Russian president Dmitri Medvedev that he would have more flexibility to negotiate if he was re-elected, Romney rattled the foreign policy establishment by calling Russia without question our number one geopolitical foe. The two statements encapsulated the candidates' differing approaches: Obama has sought a thaw in U.S.-Russian relations, while Romney remains wary of a country that continues to stymie action on Syria and Iran.

Despite Russian intransigence on Syria and a crackdown on free speech launched by President Vladimir Putin, Flournoy said the reset in relations pursued by Obama has yielded tremendous benefits. She pointed to a new arms control treaty, Russia allowing American supplies to travel through its territory en route to Afghanistan, and Russia's agreement to stop supplying Iran with some weapons.

It is important, Flournoy said, to have a cooperative relationship with Russia where our strategic interests align while not taking any action that would sell out our allies or allow Russia to have spheres of influence in Europe.

I worry if you took this approach of this is our new geopolitical foe again you'd lose some of that cooperation that's very important to American interests, she said.

Williamson warned of an authoritarian drift in Russia over the past three years and said there are ways to circumvent Russian opposition to certain international actions (Russia has joined China in blocking a U.N. Security Council resolution calling for Syria's Assad to step down).

You don't have to wait for Russia to say 'you may do this,' he said.

Defense Spending

Romney has accused Obama of trying to hollow out the American military with ruinous budget cuts. Flournoy sought to rebut that claim by separating two separate sets of budget reductions: a $450 billion cut over the next decade, proposed by the administration and agreed to by some Republicans; and an automatic $600 billion reduction, or sequester, mandated by the collapse of the deficit-cutting super committee last year. 

The president is not advocating one trillion dollars of defense cuts, Flournoy said.

The first set of cuts would simply slow the growth of the overall defense budget by accounting for the end of the wars in Iraq and Afghanistan, she said, noting that projections put the Pentagon's budget above its 2008 levels even with the reductions. This is not some devastating, radical, horrible cut in defense spending, she said.

The impending sequestration is a different matter, she said, and everybody agrees that would be very devastating for U.S. national security, and we want to avoid it at all costs.

Williamson backed Romney's plan to rebuild our Navy by building an additional 14 ships a year and rejected the current path which allows a diminution of our defense. But he dodged repeated questions from the moderator about how Romney would expand defense spending, enact tax cuts and prevent a further ballooning of U.S. debt, citing philosophical differences between Romney and Obama.

I would suggest that the president would like to have this debate about taxes versus no taxes but not go into underlying issues, Williamson said.