Remy de la Mauviniere/AP Photo

Syrian President Bashar al Assad will not be able to maintain his grip on power in the wake of a wave of opposition that has dragged on for almost a year, America's top intelligence officials told Congress today.

"I personally believe it's a question of time before Assad falls," James Clapper, director of National Intelligence, told the Senate Permanent Select Committee on Intelligence.  CIA Director David Petraeus added, "I generally subscribe to that as well."

Clapper said "it could be a long time" before the Assad regime falls because of "the protraction of these demonstrations" and a Syrian opposition that remains fragmented.  Despite that, Clapper said "I do not see how long he can sustain his rule of Syria."

Petraeus described the Syrian opposition as "showing a considerable amount of resilience" and is now carrying out increasing levels of violence.

The CIA director noted how the two main Syrian cities of Damascus and Aleppo had been relatively free of violence, but are now seeing violence in the suburbs.

He said the stiff resistance regime forces have encountered shows "how substantial the opposition to  the regime is and how it is in fact growing and how increasing  areas are becoming beyond the reach of the regime's security forces."

Both Clapper and Petraeus said it was uncertain what a post-Assad Syria might look like, though Petraeus thinks the Sunni Arab majority might emerge in the new leadership and that could raise the question of how they would deal with minority populations within Syria.

Both intelligence officials said Hezbollah and Iran are concerned about what's going on in Syria because it could affect their supply flow into Lebanon.  "What is transpiring in Syria is of course of great concern to them," said Clapper.  "It is why they are both expending great effort, in terms of resources and advice and this sort of thing, to prop up the Assad regime."

Petraeus said, "Clearly, the loss of Syria as a logistics platform, a line of  communication into Lebanon to support Hezbollah would be a   substantial setback for Iran in its efforts to use Hezbollah as  a proxy."  Adding "that is why the Revolutionary Guards Quds Force  is so is engaged in trying to prop up Bashar al Assad right  now. "

Later today, a new diplomatic push will begin at the United Nations Security Council calling for the Assad regime to end the violence against the Syrian opposition.

Secretary of State Hillary Clinton will be at the meeting and along with the British and French Foreign Ministers will speak in support of a resolution that in addition to calling for an end to the violence will ask for Assad to step aside.

The main obstacle to passage of the resolution is strong opposition by Russia  which remains Assad's most important ally.