MOSCOW, Sept. 13 - President Vladimir V. Putin ordered a stunning overhaul of Russia's political system on Monday in what he called an effort to unite the country against terrorism. If enacted, as expected, the proposals would strengthen his already pervasive control over the legislative branch and regional governments. Mr. Putin, meeting in special session with cabinet ministers and regional government leaders, outlined what would be the most sweeping political overhaul - and his most striking single step to consolidate power - in Russia in more than a decade. Critics immediately said it would violate the Constitution and stifle what...