By Phil Stewart
AMMAN (Reuters) - The top U.S. military officer told American troops in Jordan on Thursday that their mission to help the kingdom contain the fallout from Syria's war would likely last years, as the United States bolsters support for the key regional ally.
General Martin Dempsey, chairman of the Joint Chiefs of Staff, addressed a group of mostly U.S. planners who have arrived over the past several months as America expands assistance that now includes stationing F-16 fighter jets and Patriot missiles there.
The U.S. military has roughly 1,000 troops stationed in Jordan.
Dempsey told around 100 troops at a facility on the outskirts of Amman that they would be critical in helping anticipate and "shape" events on the ground. His comments came as fears mount over how massive inflows of refugees could undermine the kingdom's stability.
"We're at our best when we can actually shape events and prevent conflict," he said, noting the efforts to coordinate humanitarian relief.
"And that's another reason why you're here, (to) help us shape - understand and shape - so that we don't end up having to react to events but rather have some influence on them from the start."
Dempsey fielded questions, including on how long the mission might last, assuming the situation on the ground did not escalate. The general replied that Jordan would need to feel fully capable of dealing not only with humanitarian crises but also any threat of attack, including from extremists.
"I think we're probably talking about several years, and therefore several rotations (of troops)," he said, speaking to a group that included Army planners from the 1st Armored Division, which Dempsey led a decade ago during the Iraq war.
"We haven't actually put an end-date on it for that very reason - because it will depend how the situation evolves in Syria ... It will also depend on how our Jordanian counterparts feel about their ability to deal with these issues themselves."
Dempsey met King Abdullah and his Jordanian counterpart on Wednesday and said he would carry a request back to Washington from Amman for manned U.S. surveillance aircraft to help monitor the long border with Syria.
During his Middle East trip, which began in Israel on Monday, Dempsey has voiced concern about radical elements of the opposition fighting to remove Syrian President Bashar al-Assad. But he has expressed confidence the United States was gaining a better understanding of the moderate opposition, which Washington and its allies are looking to support.
One fear in Amman and Washington is that Islamic radicals now battling in Syria could at some point turn their sights on Jordan, particularly once the Syrian conflict ends.
"The follow-on challenge ... will be ensuring that they have a capability to defeat what will likely be a terrorist threat that will spill over at some point," Dempsey said.
"I'm not predicting that. But it's certainly a possibility - and it's one that they feel."
(Editing by Vicki Allen)