Admiral Michael Mullen, the chairman of the Joint Chiefs of Staff, said Iran "is at the heart of a great deal of discontent and disruption and instability in that part of the world.
"So I have expectations that Iran will remain front and center certainly for at least the next three to five years," he said, responding to questions after a speech at the Heritage Foundation, a conservative think tank here.
Mullen added that all options needed to be kept on the table, but "I am not arguing that that is where the next conflict occurs."
"And I would hope that in the future we could figure out a way to dialogue with them to figure out a way ahead. We've done that in the past with our enemies. We should be able to do that as well," he said.
President George W. Bush has rejected wide-ranging talks with Iran unless it first halts a uranium enrichment program that Washington suspects is part of a drive to acquire nuclear weapons.
But the United States has engaged Tehran in three rounds of ambassador level talks specifically on Iraq, and has agreed to a fourth round if the Iraq government can arrange it.
Mullen's comments follow angry charges by Washington that Iran's Revolutionary Guard Quds Force is deeply involved in arming, funding and training armed Shiite groups.
They fought government troops to a standstill in the southern Iraqi port of Basra last month, which Mullen said "really highlighted the Iranian influences in ways that some of us had not seen before as directly as occurred in that part of Iraq.
"It certainly got a lot of people's attention. And it was across the board," he said.
Separately, Pentagon spokesman Geoff Morrell told reporters: "Lord knows we found stashes and stashes of weapons in Basra a couple of weeks ago that were clearly provided by the Iranians."
"And Lord knows that the rockets and the missiles that have been falling upon the Green Zone, attacking and killing not just US personnel there, but Iraqis … that those are provided by the Iranians."
The Green Zone is the heavily fortified area of downtown Baghdad where the US and British embassies, as well as the Iraqi prime minister's office, is located.
