Andrei Sinyavsky, the outstanding literary critic and writer whose arrest and trial in 1966 was widely seen as the start of the Soviet dissident movement, died Tuesday of brain cancer at his home in a Paris suburb. He was 71. ""He is probably the most important Russian writer of the latter half of the 20th century,"" said Cathy Nepomnyashchy, a Columbia University professor and the English translator of Sinyavsky's best known work, ""Strolls with Pushkin."" Sinyavsky's independent position in literature and public affairs earned him widespread criticism from inside and outside Russia, both in the Soviet and the post-Communist eras. Yet he also enjoyed a profound respect from backers and critics alike. ""He was and remains my friend, with whom I disagreed,"" said one of the pioneers of the Russian human rights movement, Larisa Bogoraz. ""He did not care whether his friends or enemies agreed or disagreed with him.