* Rebels struggling against Gaddafi's loyalist troops (Adds Gaddafi on al Qaeda, paragraph 11; Levin on arming Libyan rebels, paragraphs 14-15)
By Missy Ryan and Susan Cornwell
WASHINGTON, March 29 (Reuters) - Intelligence on the rebel forces battling Libyan leader Muammar Gaddafi has shown "flickers" of al Qaeda or Hezbollah presence but there is still no detailed picture of the emerging opposition, NATO's top operations commander said on Tuesday.
"We are examining very closely the content, composition, the personalities, who are the leaders of these opposition forces," Admiral James Stavridis, NATO's supreme allied commander for Europe and also commander of U.S. European Command, said during testimony at the U.S. Senate.
Gaddafi's troops on Tuesday reversed the westward charge of rebel forces as world powers met in London more than a week after the United States and other nations launched a military campaign aimed at protecting Libyan civilians.
While Stavridis said the opposition's leadership appeared to be "responsible men and women" fighting Gaddafi, he said that "we have seen flickers in the intelligence of potential al Qaeda, Hezbollah. We've seen different things."
"But at this point I don't have detail sufficient to say there is a significant al Qaeda presence or any other terrorist presence," he said.
The Pentagon says it is not communicating officially with the Libyan rebels.
U.S. Ambassador to the United Nations Susan Rice disagreed that al Qaeda was involved in the rebel movement.
"I would like to think I'm reading much of the same stuff and no," Rice told Fox News when asked whether she had seen any evidence to support Stavridis' assessment.
"I think we can't rule out the possibility that extremist elements could filter into any segment of Libyan society and it's something clearly we will watch carefully for," she added.
The United States has appointed veteran diplomat Chris Stevens as envoy to the Libyan rebels in Benghazi and expect him to go there soon to get a "clearer picture" of the rebel leadership, U.S. officials said. France has also dispatched an envoy to Benghazi, a diplomatic source said.
Gaddafi has said that al Qaeda sleeper cells were behind the uprising, that those opposed to his rule had been brainwashed by Osama bin Laden and that their milk and coffee had been spiked with hallucinogenic drugs.
'MORE CLARITY' NEEDED FOR EXIT PLAN
Stavridis' comments came a day after President Barack Obama made his case for action in Libya in a televised address to Americans, who are wary of another war with U.S. troops already in Afghanistan and Iraq.
While Obama has said Gaddafi should leave power, he stressed the military mission endorsed by the United Nations was limited to protecting civilians and enforcing a no-fly zone over Libya.
Senate Armed Services Committee Chairman Carl Levin said he believed the Obama administration was considering the pluses and minuses of arming the Libyan rebels. Levin said consensus with U.S. allies would be needed on the matter since NATO had agreed to take charge of the military mission in Libya.
"I believe he (Obama) will continue to weigh carefully the pros and cons of providing offensive arms such as heavy vehicles and artillery to the opposition," Levin said at the hearing where Stavridis was testifying.
Even as the rebels struggle against Gaddafi's better-armed, better-organized troops, Stavridis said the long-time Libyan leader was likely to go if the coalition brought a range of military power to bear against him.
"If we work all the elements of power, we have a more than reasonable chance of Gaddafi leaving, because the entire international community is arrayed against him," he said.
Senators' questions about the make-up of the Libyan opposition reflect skepticism in Congress about U.S. preparedness for the campaign. It also underscores worries about who might take over in Libya if Gaddafi does go.
"It's premature to say what is our exit strategy until we have a little more clarity moving forward," Stavridis said.
The Libya campaign has also intensified fears in Congress about the high cost of military activities overseas.
The war in Afghanistan costs the United States around $9 billion a month. Stavridis said the Libya mission had cost "hundreds of millions of dollars" so far. (Writing by Missy Ryan; Editing by John O'Callaghan, Deborah Charles and Eric Walsh)