LAUSANNE, Switzerland — The United States is considering letting Tehran run hundreds of centrifuges at a once-secret, fortified underground bunker in exchange for limits on centrifuge work and research and development at other sites, officials have told The Associated Press. The trade-off would allow Iran to run several hundred of the devices at its Fordo facility, although the Iranians would not be allowed to do work that could lead to an atomic bomb and the site would be subject to international inspections, according to Western officials familiar with details of negotiations now underway.