WASHINGTON — US Vice President Joe Biden told a packed AIPAC conference on Monday that America's commitment to Israel remained ironclad, and implied that the White House is preparing for the possibility of confrontation with Iran over its nuclear program."President Barack Obama is not bluffing," Biden said, noting that the administration is not actively looking for war with the Islamic Republic. "God forbid the need to act occurs, it's critically important for the whole world to know we did everything in our power to avoid confrontation. God forbid we have to act, its important that the whole world is with us."The administration's firm position, he said, "is to prevent Iran from acquiring a nuclear weapon, period. End of discussion. Not contain: prevent."Biden addressed growing criticism on US policy toward Syria, charging back that the White House position on Syria is clear: Assad must go, and the use or transfer of chemical weapons— by any party involved in the conflict— was an American red line."We are not signing up for one murderous gang replacing another in Damascus," he added.In a preview of President Obama's upcoming visit in late March, the vice president said he wouldn't prompt policy introductions. But he said the president would be outlining a renewed interest in the currently stalled peace process."We make no apologies for continuing to pursue that goal," the vice president said. "It takes two to tango, and the rest of the Arab world has to get in the game. We're under no allusions about how difficult it will be to achieve.""We've always disagreed on tactics, but ladies and gentlemen, we've never disagreed on the strategic imperative," Biden said.