WASHINGTON // A senior State Department official said yesterday that he expects Iran to reject a U.N.-backed entreaty to end its nuclear enrichment program and added that the United States will quickly press for international sanctions against Tehran if an Aug. 31 deadline is not met. Undersecretary of State R. Nicholas Burns, the Bush administration's point man on Iran, said the United States has the backing of fellow permanent members of the United Nations Security Council for economic and diplomatic sanctions and will push for them to be imposed early next month if Iran does not halt uranium enrichment at...