Vienna, Austria ? He’s running unopposed, but Mohamed ElBaradei may still fail in his bid for a third term leading the U.N. nuclear watchdog agency, tripped by his main opponent, the United States.

Unable to find a candidate willing to oppose the independent-minded Egyptian diplomat, Washington now is quietly lobbying other member states in ElBaradei’s International Atomic Energy Agency in a bid to unseat him by June, opening the way for a replacement more to the Bush administration’s liking — one harder on Iran and other nations on the U.S. nuclear threat list.

With the agency spearheading international attempts to squelch nuclear proliferation, who controls the IAEA is key for Bush administration officials. They want someone sharing their view of which countries represent nuclear threats.

ElBaradei has challenged those views — particularly over prewar Iraq and Iran, both labeled part of an “axis of evil” with North Korea by President Bush.

He first disputed U.S. assertions that Saddam Hussein had an active nuclear weapons program — claims that remain unproven. He then refused to endorse assertions by Washington that Iran was working to make nuclear weapons. Tehran says its nuclear program is for generating electricity.

U.S. officials in Vienna and Washington refuse to discuss Washington’s strategy in toppling ElBaradei. But diplomats accredited to the Vienna-based IAEA say America has a new candidate in the wings, who will be presented if the United States swings enough nations on the IAEA board of governors to back its demand for a no-confidence vote in the incumbent.