A U.S. trade agency on Tuesday banned the sale of several iPhone and iPad models for infringing a Samsung patent, dealing a high-profile setback to Apple’s crusade against copycats. If upheld, the ruling would show that at least some of Apple’s iconic technology duplicated that of its primary competitor in the mobile-device market, an embarrassment for a company that has held itself up as the source of Silicon Valley’s most groundbreaking innovations. Samsung, once a bit player in the cellphone market, now sells more smartphones than Apple around the world. The order by the U.S. International Trade Commission (ITC) would block sales of several older devices that work on AT&T Wireless’s network, including the iPhone 4, the iPhone 3GS and the iPad 2 3G.