In a rare victory for environmentalists, a Connecticut judge issued an order barring the restarting of the Millstone 2 nuclear reactor on Long Island Sound, just one day before the generator was to produce commercial power for the first time in three years. Robert W. Bishop, the general counsel of the Nuclear Energy Institute, a trade groupb for the nuclear power industry, said this was apparently the first time a court had prevented the restarting of a nuclear plant once it had received its operating permit.