HANOI (Reuters) - Vietnamese police have arrested a dissident accused of attempting to overthrow the government, the communist state s official website said on Wednesday, bringing to at least 17 the number of dissidents arrested this year. Tran Thi Xuan, 41, was arrested in the northern province of Ha Tinh on Tuesday. The website did not give details of the alleged crime. Reuters was unable to contact her and it was not clear whether she had a lawyer. Despite sweeping economic reforms and growing openness to social change, the Communist Party tolerates little criticism.     The crackdown on dissent follows changes in the ruling party hierarchy early last year which gave greater influence to the security establishment.