The loud argument Thursday night between Vice President Biden and Rep. Paul Ryan over foreign policy revealed in the end just how little separates the presidential tickets when it comes to how the United States should engage the world.

A vice-presidential debate should rarely serve as a substitute for what the top of the ticket thinks on foreign policy. After all, the president, with varying degrees of say from his elected deputy, decides the course for the United States in the world.

But the debate at Centre College provided the first extensive foray into foreign policy of this debate season, and the answers delivered by the candidates closely reflect what their principals, President Obama and former Massachusetts governor Mitt Romney, have said on the same subjects with only slight differences in emphasis.

In that way, the Biden-Ryan exchanges offer clues to Obama’s future approach and Romney’s likely line of criticism heading into their Oct. 22 debate on foreign policy, the final time the two candidates will appear on the same stage before Election Day.

On one level, Biden carried the message that Obama has sought to deliver in ending the U.S. involvement in Iraq and in announcing a timeline to conclude the Afghanistan war: It is time for the United States to brings its forces home and spend the savings here.

Ryan, too, emphasized Romney’s main critique of Obama’s foreign policy: That it has reduced U.S. influence abroad, confused some traditional allies and too carefully managed antagonists such as Russia’s Vladi­mir Putin, Syria’s Bashar al-Assad and Iran’s ruling clerics.

He also hit Biden hard on the administration’s changing story over the Sept. 11 attack on a too-lightly protected U.S. diplomatic post in Benghazi, Libya, in which Ambassador J. Christopher Stevens and three other Americans were killed.

It appeared to be that foreign policy question, coming right out of the gate, that Biden had the most trouble addressing, as he said that “we did not know” about the rising security concerns of the U.S. mission in Libya in real time.

At the Friday news briefing, White House spokesman Jay Carney said Biden “was speaking directly for himself and for the president,” not the State Department agencies that handled a request for more security in Libya. Carney said Biden “meant the White House” did not know of the request, not the administration more broadly.

Ryan also added a note of caution to his ticket’s foreign policy approach that has been largely absent from Romney’s speeches, which have emphasized U.S. power and the need to promote freedom around the world.

In response to moderator Martha Raddatz’s question concerning his criteria for military intervention, Ryan noted that “each situation will come up with its own set of circumstances.”

Obama’s foreign policy has also been defined by a largely ideology-free, case-by-case management of crises and opportunities that has led to what Republicans have criticized as inconsistency, citing the assertive U.S. intervention in Libya but a far more cautious handling of the bloodier conflict in Syria.

Asked whether he would ever intervene militarily for humanitarian reasons, Ryan said, “If you are talking about putting American troops on the ground, only in our national security interests.”

Much of what appeared to be a split between Biden, the former chairman of the Senate Foreign Relations Committee, and Ryan, the current chairman of the House Budget Committee, had more to do with the theatrics of the encounter than the substance of their answers.

Biden sighed and groaned at times as Ryan characterized the Obama administration foreign policy — and Biden's role in it, mostly in managing the Iraq portfolio. Romney has said he would have left several thousand U.S. troops in Iraq after the 2011 deadline for full withdrawal, set by the George W. Bush administration.

Ryan criticized Biden on Thursday for failing to secure an agreement to allow that to happen, despite public approval of the departure. He also ranged lightly over a broad swath of geopolitical landscape — hopping from crisis to aggrieved ally to crisis — in an attempt to portray, in his words, “the unraveling of the Obama foreign policy.”

Beyond that, the similarities on the specifics were far more evident than the differences. And much of the agreement coalesced around what is already Obama foreign policy.

On Iran’s nuclear ambitions, Ryan spoke more stridently about the possibility of war — and was chided for his “loose talk” by Biden.

But the differences were largely technical, focusing on the timeline outlined recently at the United Nations by Israeli Prime Minister Benjamin Netanyahu, who said that by next summer Iran will have everything it needs to build a nuclear weapon.

Neither candidate ruled out a military strike to prevent that from happening, and amid warnings of a Middle East arms race, neither man mentioned that Israel already has an undeclared nuclear arsenal.

Ryan pronounced in starker terms that a nuclear-armed Iran would be “worse” than another Middle East war involving the United States, mostly because of the threat it would pose to Israel.

By saying, as he did at the United Nations last month, that the United States would “do what it takes” to prevent Iran from developing a bomb, Obama effectively, if less pointedly, has said the same thing.

The heart of the Romney-Ryan approach to Iran remains international sanctions, which Obama, who has made nuclear nonproliferation a priority of his foreign policy, has tightened throughout his administration.

There is increasing evidence inside Iran that the sanctions are creating the kind of economic hardship that the Obama administration hopes will generate pressure on Iran’s government to give up its uranium-enrichment program.

“He sees the economy going into free-fall,” Biden said, referring in shorthand to Iran’s supreme leader, Ayatollah Ali Khamenei.

Ryan also endorsed the Obama-Biden timeline for leaving Afghanistan at the end of 2014, saying, “We don’t want to stay.”

The main differences that the Republican candidate raised were over the pace of withdrawal of Obama’s 30,000 surge forces, and Ryan’s contention that he and Romney would defer more to generals in making those decisions.

Those are largely tactical differences, not strategic ones.

But Biden, who showed a firmer grasp of the Afghan exit strategy than Ryan, used the issue to deliver a politically popular message to a war-weary country.

“We’re sending in more Afghans to do the job,” Biden said.

One of the main differences between Obama and Romney is over the question of whether to help arm Syria’s rebels.

Citing the brutal government campaign against rebel forces and their civilian supporters, as well as the blow that losing Assad would deal to Iran, Romney has said he would send weapons, including arms to strike tanks and aircraft.

Obama, concerned that more guns would escalate a civil war already spilling across Syria’s borders, has declined to do so. His concern, in part, is that too little is known about Syria’s rebel forces to arm them, given that they may soon run a country on Israel’s doorstep in the heart of the Middle East.

Biden took the difference to an alarming place Thursday, suggesting that Romney and Ryan might be considering direct military intervention in Syria, even though neither has said that before.

“The last thing America needs is another ground war in the Middle East, requiring tens of thousands, if not well over 100,000 American forces,” Biden said, likely using “ground war” as a way to distinguish from what could be an air campaign against Iran’s nuclear sites.

Ryan bluntly ruled out sending in U.S. troops, something that would likely be hugely unpopular as the last of two long U.S. wars in Muslim countries winds down.

He focused his criticism on the overall Obama-Biden approach to Syria, which he said had been dictated too much by Russian recalcitrance and unsuccessful U.N.-sponsored peace efforts. As Romney has done before, Ryan used the Obama-Biden policy to talk about what he has called “weak leadership.”

“We gave Russia veto power over our efforts through the U.N.,” Ryan said. “And meanwhile, about 30,000 Syrians are dead.”

It was unclear, however, how Ryan — if elected — intends to manage Russia, which holds a veto-wielding seat on the U.N. Security Council. Biden indicated that the Russian role was something that had to be taken into account, like it or not.

“With regard to the reset not working, the fact of the matter is that Russia has a different interest in Syria than we do,” Biden said. “And that’s not in our interest.”