A Moscow cop is left out in the cold in this "impressive" Edgar Award winner for Best Mystery Novel ( The Washington Post Book World).   When forced to choose between the law and the party line, Police Inspector Porfiry Rostnikov has a disturbing tendency to fight for justice, and that has won him no friends at the Kremlin. Now his enemies in the KGB have arranged a transfer to the lowest rungs of Moscow law enforcement, a backwater department assigned to only the most hopeless cases, one of which is about to take Rostnikov deep into Siberia.   A corrupt commissar has been stabbed through the eye with an icicle. A murder at this level should be a top priority, but Rostnikov gets the distinct impression that the powers-that-be would prefer this case go unsolved—and that Rostnikov not survive this Siberian winter.   "As always, Kaminsky provides a colorful, tightly written mystery . . . filled with twists, countertwists, and a surprise ending that is plausible and clever." — Chicago Tribune