TEHRAN, Iran — The United States barred Tehran's pick for its new U.N. envoy on Tuesday, a day after American lawmakers voted against letting the diplomat enter the country. American officials objected to the selection of Hamid Abutalebi because of his alleged participation in a group that held 52 Americans hostage for 444 days in the 1979 seizure of the U.S. Embassy in Tehran.The Obama administration has stopped short of saying it would refuse him a visa. "The U.S. government has informed the government of Iran that this potential selection is not viable," White House spokesman Jay Carney said in Washington.