By Elise Labott
Key meetings this week on Syria will try to figure out how the Obama administration can help moderate heavy rebel casualties and stem opposition defections to radical groups as the prospect for a political solution to the civil war grows dim.
Recent gains by the regime in Qusayr and its ongoing offensive to retake areas of Aleppo - all with the help of Hezbollah fighters - has created an urgency in the administration to act before President Barack Obama's stated policy objective of ousting Syrian President Bashar al-Assad is lost.
"It's really bad but whether this is fatal, we don't' know," one senior administration official said of recent gains by regime forces. "There is a recognition that unless we provide help, a lot of help, the situation is going to be very, very terrible."
Officials say in numerous conversations with U.S. Ambassador to Syria Robert Ford and other officials, Salim Idriss, the commander of the rebel Free Syrian Army, described a dire situation. He pleaded for weapons and ammunition to stop both causalities and defections to radical groups like Jabat al-Nusra.
"He said he is losing people left and right, either being killed by the regime or being recruited by al-Nusra," one administration official said. "The situation for the moderate opposition, according to Idris, is very grave.
Discussions this week, including a meeting of the National Security Council principals on Wednesday, will center around whether to provide arms to vetted, moderate rebel units.
Although debate continues about a possible "no-fly" zone, officials said there is a reluctance to commit the kind of resources that would be needed to counter the regime's air defenses, when the majority of the fighting is on the ground.
"A 'no-fly' zone doesn't get you much," the senior official said. "There simply isn't enough being done from the air."
The official described a "somber mood" among Syria hands throughout the administration, who remain frustrated at the inaction by the Obama administration in the face of a deterioration on the ground in Syria and spillover to neighboring states like Lebanon.
Administration officials spent much of the past weekend studying the implications of the devastating defeat of opposition forces in Qusayr.
A senior administration official tells CNN that, even after all the anlysis, "we just flat don't know" what it means for the rebels.
"Is it sort of the end of the road for these guys?" the official said. "I hope it isn't but there's no question that substantial re-supply is going to be necessary in order for the Free Syrian Army to be able to hold their own," the official said.
At Qusayr it was notable, the official says, how little Syrian Army forces loyal to al-Assad were directly engaged, "except from the air."
Instead, militias from Lebanon, Iran and Iraq did most of the fighting.
"I think there's no question that Qusayr was a very serious negative point for the Syrian opposition, for the Free Syrian Army," the official says. "Principally because they were facing, for the first time, major Hezbollah fighters as well as Iraqi militia, as well as Iranian militia. They just couldn't overcome that."
The rebels need weapons and ammunition, the official says, "and they need a lot more of it."
While Obama is said to be inching closer toward arming the rebels, officials and experts wondered whether he would ultimately decide to do that with things getting worse.
"Think of the implications for the neighborhood and the region. We have refugees, radicals in Syria and spillover and radicals in the neighborhood," another senior official said. "Everyone knows unless we do something, and fast, it will be untenable for the U.S. But is government ready to make these political decisions?"
Meanwhile, planning for a conference in Geneva to bring together members of the opposition and the regime to discuss a political transition has taken a back seat as the administration turns its attention to the worsening situation on the ground.
The conference had been postponed while the opposition tried to unite and choose its leadership, but officials said it was an almost certainty the opposition would not attend, even if it was organized, because of the situation on the ground.
"I think Geneva is on a slow roll at the moment," the senior official said. "I think it has to be."
CNN's Jill Dougherty contributed to this report.