WASHINGTON (Reuters) - The Bush administration's tacit support for Israeli military strikes on Lebanon may have increased the danger of militant retaliation against the United States and U.S. interests abroad, some experts say.

U.S. and European authorities have stepped up vigilance against groups including Hezbollah, which intelligence experts say has cells in North America, South America, Europe, Africa, Asia and the Middle East.

Israel's attempt to cripple Hezbollah in Lebanon may have strengthened the Shiite organization by winning it fresh political support among moderate Arabs and Muslims, former officials and other experts said.

The Bush administration's stance that calling an immediate cease-fire would not be productive has also angered many Arabs at a time when bombings in Lebanon are causing large numbers of Muslim civilian casualties, they added.

Washington claims it is supporting long-term efforts against terrorism in the region.

One European counterterrorism official said it was widely recognized there that Middle East hostilities could become a motivating factor for Sunni groups inspired by Osama bin Laden who ordinarily dislike Hezbollah but might try to exploit the outrage in Arab communities.

"Even al Qaeda itself may be ready with an attack, and they may choose to use it now," said Michael Scheuer, a former CIA counterterrorism official who ran the agency's bin Laden unit.

But Peter Brookes of the Heritage Foundation, a conservative think tank, said the Middle East crisis had not increased the already tangible danger of attack. "We've always been a target, and Hezbollah already has American blood on its hands," Brookes said.

Growing danger

Some former intelligence officers were adamant about a growing danger, however.

"There will be revenge attacks," said one former U.S. official, who remains up to date on counterterrorism strategy. "The concern now is that there's rising animosity that will be exploited, not just by Hezbollah," said the former official, who spoke on condition of anonymity, adding: "Then there are people being driven over the edge by what's happening, who aren't necessarily members of any group, but who might strike."

Hezbollah had roles in a number of attacks on American targets in the 1980s and 1990s, including the 1983 barracks bombing that killed 241 U.S. Marines, Navy personnel and Army soldiers in Beirut, according to the State Department.

But intelligence officials said the group was believed to have suspended hostilities against the United States in the 1990s and said there was no sign Hezbollah had changed its policy.

Hezbollah leader Sayyed Hassan Nasrallah has made no threats against the United States in a recent series of speeches and media interviews.