AP Diplomatic Writer
WASHINGTON (AP) -- Of all the interests backing President Barack Obama's call for Congress to authorize military strikes on Syria, perhaps none is more concerned about the prospect of a "no" vote than America's pro-Israel lobby, which is finding it difficult to overcome widespread opposition to the use of force.
Considered to be some of the most influential lobbyists on Capitol Hill, officials with several pro-Israel groups say they are running into rare resistance from lawmakers, even among staunch Israel advocates on whose support they could almost unquestionably count in the past.
The administration has sought and won support for the vote from most of the major pro-Israel groups that traditionally have been most effective in promoting legislation to enhance Israel's security.
Among those that have released public statements and made private calls to lawmakers to urge them to vote "yes" are The American-Israeli Public Affairs Committee, or AIPAC, the Anti-Defamation League and the Simon Wiesenthal Center.
"There is no question that it is very challenging," said an official from one, who spoke on condition of anonymity because he is not authorized to speak publicly on behalf of the organization. "It is an extremely challenging environment right now."
The crux of their argument is that inaction will undermine American credibility in limiting the development and use of weapons of mass destruction with a direct impact on Israel's security, particularly as it relates to Iran and its nuclear program.
Israel regards Iran as an existential threat, and preventing Tehran from developing nuclear weapons is its primary national security concern. Iran says its program is for peaceful purposes.
Lobbyists also acknowledge that a U.S. military strike could risk Israel becoming a retaliatory target of Syrian-backed Hezbollah or other groups acting on Assad's behalf. But they say that risk is smaller than the risk of letting Assad go unpunished.
"This critical decision comes at a time when Iran is racing toward obtaining nuclear capability," AIPAC said in its statement. "Failure to approve this resolution would weaken our country's credibility to prevent the use and proliferation of unconventional weapons and thereby greatly endanger our country's security and interests and those of our regional allies."
"AIPAC maintains that it is imperative to adopt the resolution to authorize the use of force and take a firm stand that the world's most dangerous regimes cannot obtain and use the most dangerous weapons," it said.
The Anti-Defamation League urged Congress to "act swiftly to add its voice to hold (Assad) accountable for the wanton slaughter of his own citizens."
"Any nation that violates international norms and obligations which threaten the peace and security of the world must face the consequences of those dangerous acts," it said.
In making their case for military action to punish Syria for using chemical weapons, Obama and his aides have gone out of their way to court the support of the American Jews by drawing parallels between Syrian President Bashar Assad's use of poison gas and the gas chambers of Nazi Germany.
Visiting the Great Synagogue of Stockholm on a trip to Sweden last week, Obama alluded to the connection while paying tribute to Raoul Wallenberg, the Swedish diplomat credited with saving at least 20,000 Jews during the Holocaust.
"Because he refused to stand by, Wallenberg reminds us of our power when we choose not simply to bear witness, but also to act," Obama said.
He later added, "I cannot think of a better tribute to Raoul Wallenberg than for each of us, as individuals and as nations, to reaffirm our determination to live the values that defined his life and to make the same choice in our time."
Secretary of State John Kerry has invoked the phrase "never again," a direct reference to international vows to prevent a repeat of the Holocaust, and even compared Assad to Adolf Hitler, something that even the pro-Israel groups backing the administration have shied away from, at least so far.
Despite winning universal condemnation of Assad for using chemical weapons, the administration has found its arguments are not convincing skeptical lawmakers and their war-weary constituents that military action is a moral imperative.
"I think Israel has a strong natural defense and I think they can do well in any battle. But I don't want to involve Israel in a battle because they have so many enemies around them that I'm fearful it can spin out of control," Sen. Rand Paul, R-Ky., told Sean Hannity of Fox News last week.
Officials with several pro-Israel groups say they are encountering the same problem, which is compounded by pure political motivations, especially among Republicans, for opposing Obama's request.