The contacts so far are not extensive, and officials say Iranian-backed Hezbollah has plenty of reasons, both ideological and practical, to spurn any formal advances from al Qaeda's leadership.
Instead, U.S. counterterrorism officials say individual al Qaeda members, cut off from the group's leadership by the U.S. military operation in Afghanistan, are turning to what they consider the next best thing — Hezbollah, which is based in Lebanon.
Still, the prospect of cooperation at any level has alarmed U.S. officials.
The fervor and international sophistication of al Qaeda members, coupled with the resources, organization and state backing of Hezbollah, would constitute a volatile mix, terrorism experts said.
Intelligence indicates that "al Qaeda (operatives), because they have been disrupted, are looking for places to go for help with various support functions," a senior law enforcement official said, speaking on condition of anonymity.
"Hezbollah has a very extensive support network, not only in the Mideast, but in Europe, and in the United States," the official said.
Hezbollah was formed in 1982 with Iranian backing during Israel's invasion of Lebanon. The group is linked to the bombing of the U.S. Marine barracks in Lebanon in 1983 that killed 241 Americans, bombings of two U.S. Embassy buildings and kidnappings of more than 50 foreigners.
Most of its recent operations have been directed at Israel, rather than the United States.
There is some evidence suggesting Hezbollah members have shared intelligence on U.S. efforts to track terrorists in certain cities and provided some financial assistance, a law enforcement official said, speaking on condition of anonymity.
But that conclusion isn't universally accepted throughout the U.S. government — underscoring the difficulty of gathering solid intelligence on the two terrorist groups.
Other U.S. counterterrorism officials told The Associated Press that while they have observed increased contacts and relationship-building between members of the two terror groups, they haven't seen credible evidence of financial or operational collaboration.
FBI counterterrorism agents believe many al Qaeda members are desperate for resources because of U.S. efforts to reduce the funds available to the terrorist organization.
Despite the low-level meetings, U.S. officials are unaware of high-level contacts between al Qaeda's surviving leadership and that of Hezbollah. They have denied news reports that al Qaeda leaders attended a March meeting of Hezbollah officials in Lebanon.
Yet Lebanon has been the site of many of the al Qaeda contacts with Hezbollah that U.S. officials have learned about, one U.S. counterterrorism official said.
One senior al Qaeda leader — Abu Musab Zarqawi — is known to have fled Afghanistan for Hezbollah's sometime master, Iran. He stayed there briefly after the U.S. began bombing Afghanistan, but has since left, U.S. intelligence officials say. There are no signs that Iran's government has sanctioned recruitment of al Qaeda castoffs.
Hezbollah also enjoys support from Syria and Lebanon, both of which have aided the U.S. war on al Qaeda, and U.S. officials believe Hezbollah's relationship with both countries could be threatened if it began working extensively with bin Laden's group.
"Hezbollah leaders understand that al Qaeda is too hot to touch right now," said Janice Paine, a terrorism expert at Harvard University. "It's very easy for Hezbollah leaders to imagine the bombs that are falling on al Qaeda could be falling on them if they get connected to any terrorism in the United States.
"A connection between the groups would also undo the work that some Hezbollah leaders have done to make the group seem more moderate," Paine said.
Hezbollah's leadership is known to have been surprised by the Sept. 11 attacks on the Pentagon and World Trade Center.
Historically, al Qaeda and Hezbollah functioned separately. Al Qaeda is run by Sunni Muslims and Hezbollah by Shiites.
Ideological differences between these chief two branches of Islam apparently have prevented an alliance thus far, but their mutual hatred of America and Israel may drive them closer, officials fear.
Numerous Al Qaeda members have made their way to the Mideast since the destruction of bin Laden's Afghan operations, said Stan Bedlington, a former terrorism analyst at the CIA. Arabs like Hezbollah because it has been regarded as victorious since the Israeli military pulled out of south Lebanon in 2000.
"With three groups (Hezbollah, al Qaeda and the Palestinian group Hamas) in the same territory, some contact is inevitable," Bedlington said.