Rebel forces in Libya that have sought to take advantage of U.S.-backed airstrikes appear to include a small number of fighters with ties to al-Qaeda, American officials said Tuesday.

The disclosure raises a potential complication for the Obama administration and other Western governments that are weighing whether to provide arms and other support to Libyan opposition groups, whose composition in some cases remains unclear.

U.S. officials played down their concern about al-Qaeda’s presence, saying that its numbers appear negligible and that the terrorist network has had no dis­cern­ible influence on the groups seeking to oust Libyan dictator Moammar Gaddafi.

“We have seen flickers in the intelligence of potential al-Qaeda” and Hezbollah fighters among opposition forces, U.S. Adm. James Stavridis, NATO’s supreme allied commander for Europe, said in congressional testimony.

But Stavridis stressed that emerging intelligence on the Libyan opposition “makes me feel that the leadership that I’m seeing are responsible men and women who are struggling against Colonel Gaddafi.”

Stavridis’s comments marked the first time a senior U.S. official had publicly acknowledged an al-Qaeda presence among rebel forces, although experts have pointed to long-standing ties between the terrorist network and Libyan opposition groups.

“It’s almost a certitude that at least part” of the Libyan opposition includes members of al-Qaeda, said Bruce Riedel, a former senior CIA analyst and adviser to President Obama. Riedel said that anti-Gaddafi elements in the rebel stronghold of Benghazi have had “very close associations with al-Qaeda” dating back years.

“I would hope that we now have a good sense of the opposition in Libya and can say that this is 2 percent, not 20 percent,” Riedel said. “If we don’t, then we are running the risk of helping to bring to power a regime that could be very dangerous.”

The prospect of an overthrow of Gaddafi dimmed somewhat Tuesday as rebels retreated from positions they had briefly recaptured with the help of allied airstrikes against Libyan air and ground elements.

Lingering questions about the composition of the anti-Gaddafi fighters may help to explain U.S. reluctance to provide weapons to the Libyan opposition. In an interview with NBC News, Obama declined to say whether the administration would arm the rebels.

Secretary of State Hillary Rodham Clinton, after meeting Tuesday with a key Libyan opposition figure in London, said the administration had “not made any decision” on the issue.

Clinton praised the rebels’ professed “commitment to democracy” but acknowledged that U.S. and allied governments have a limited understanding of who they are working with.

“We do not have any specific information about specific individuals,” she said in response to a question about concerns over al-Qaeda. “But of course, we’re still getting to know those who are leading the Transitional National Council,” which could be charged with installing a new government if Gaddafi is overthrown.

Clinton and other U.S. officials have met with key Libyan opposition figures, including Mahmoud Jibril, a former member of the Gaddafi regime who earned a PhD in political science at the University of Pittsburgh.

But others who claim to be playing leadership roles are virtual unknowns, including a man who has identified himself as a rebel leader named Abdel-Hakim al-Hasidi.

In news accounts, Hasidi has said that he fought against “the foreign invasion” of Afghanistan before being captured in Pakistan in 2002. Now, he said, he leads a force in Libya that includes members of al-Qaeda. U.S. officials said they could find no information to confirm Hasidi’s identity or any of his assertions.

Libya has for years been a fertile recruiting ground for al-Qaeda. Libyans have served in senior ranks of the terrorist network and streamed into Iraq in disproportionately large numbers to carry out attacks on U.S. forces. The Libyan Islamic Fighting Group, an enemy of Gaddafi’s, formally joined al-Qaeda in 2007.

Staff writer Karen DeYoung and staff researcher Julie Tate contributed to this story.