WASHINGTON — The six-month deal between U.S.-led negotiators and Iran will make an Iranian atomic bomb more likely, not less, because it significantly strengthens the very regime in Tehran that so desperately wants nuclear weaponry. In essence, the agreement undercuts the premise on which years of mounting economic and financial sanctions against the Islamic Republic had rested — that sanctions would force the regime to choose between its nuclear aspirations and its own survival and, in the end, it would pragmatically choose the latter. By providing $7 billion in sanctions relief — including more than $4 billion in oil revenues that are frozen in foreign banks — the agreement will give the regime significant breathing room by preventing an economic collapse, thus boosting the spirits of its disgruntled citizenry.