TEHRAN, Jan. 18 — Iran’s outspoken president, Mahmoud Ahmadinejad, appears to be under pressure from the highest authorities in Iran to end his involvement in its nuclear program, a sign that his political capital is declining as his country comes under increasing international pressure. Just one month after the United Nations Security Council imposed sanctions on Iran to curb its nuclear program, two hard-line newspapers, including one owned by the supreme leader, Ayatollah Ali Khamenei, called on the president to stay out of all matters nuclear. In the hazy world of Iranian politics, such a public rebuke was seen as...