By Alina Selyukh WASHINGTON (Reuters) – Data thefts at U.S. retailers have rekindled enthusiasm in Congress for a single federal law on how customers should be notified about such breaches, but those efforts face the same roadblock as in the past: dozens of overlapping state laws already in place. Congressional hearings and calls for new powers by consumer protection agencies followed quickly after breaches at retailers Target Corp, Neiman Marcus and Michaels Companies were revealed. And the same hurdles to reaching agreement in the past remain powerful obstacles, notably the question of whether or how the federal law would trump, or pre-empt, state regulations. Pre-emption is going to be a major part of discussions, Representative Lee Terry, a Nebraska Republican working on a data security bill in the House of Representatives, said last week after a hearing on the data breaches.