WASHINGTON — 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-Qaida, 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-Qaida’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 Gadhafi.

“We have seen flickers in the intelligence of potential al-Qaida” 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 Gadhafi.”

Stavridis’s comments marked the first time a senior U.S. official had publicly acknowledged an al-Qaida 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-Qaida, said Bruce Riedel, a former senior CIA analyst and adviser to President Obama. Riedel said that anti-Gadhafi elements in the rebel stronghold of Benghazi have had “very close associations with al-Qaida” 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 Gadhafi 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-Gadhafi fighters may help to explain U.S. reluctance to provide weapons to the Libyan opposition. In an interview with “NBC Nightly News,” Obama declined to say whether the administration would arm the rebels.

Secretary of State Hillary Rodham Clinton said the administration had “not made any decision” on the issue.