ISTANBUL (Reuters) - Almost two thirds of Turks believe U.S.-based Muslim cleric Fethullah Gulen was behind a failed coup attempt in Turkey on July 15, a survey conducted by pollster Andy-Ar showed on Tuesday, backing the government line.

President Tayyip Erdogan says Gulen, who has many followers in Turkey, masterminded the plot, having long accused his former ally of building a network within the army, police, judiciary, civil service, education and media to control the state.

Turkey wants the United States to extradite Gulen, while Washington has said it will do so only if there is clear evidence. The cleric, who has lived in self-imposed exile there since 1999, says the coup may have been orchestrated by Erdogan.

The Andy-Ar survey showed 64.4 percent of respondents believed Gulen was behind the coup attempt, while 3.8 percent blamed the United States, 3.6 percent foreign powers and 2.2 percent President Tayyip Erdogan.

That could help Erdogan consolidate his power. Critics of Erdogan fear he is using the abortive coup to wage an indiscriminate crackdown on dissent.

Turkish authorities have launched a series of mass purges of the armed forces, police, judiciary and education system, targeting followers of Gulen, who operates an extensive network of schools and charitable foundations.

The survey showed 72.6 percent of respondents thought other states supported military officers who carried out the coup, while 78.9 percent viewed the solidarity between Erdogan and opposition leaders during the coup attempt was genuine.

It also showed 83.9 percent of respondents watched Erdogan's initial comments on the night of the coup attempt and that 65.7 percent of people or a relative of theirs went out onto the streets after Erdogan's call to do so.

Asked if they wanted Gulen to be brought to Turkey, 81.5 percent of respondents said 'yes', while 77.7 percent thought Gulen and his sympathizers constitute a threat to the present order and future of Turkey.

The study was done by phone interviews with 1,496 people on July 19, Andy-Ar said.

(Writing by Daren Butler; Editing by Michael Georgy and Andrew Heavens)