PARIS, June 25 (Reuters) - A close confidant of President Jacques Chirac was named speaker of the National Assembly lower house of parliament on Tuesday, reinforcing Chirac's grip on a legislature that he hopes will push through rightist reforms.

Ex-Interior Minister Jean-Louis Debre was named to the post with 342 of 531 deputy votes in the first session of parliament dominated by conservatives after they trounced the Socialist-led former government in legislative elections this month.

Overtly declaring himself Chirac's favourite for the post, Debre easily fought off a bid by another centre-rightist, ex-Prime Minister Edouard Balladur, who ran as an independent.

Balladur withdrew his candidacy after scoring less than Debre in the first round of voting. Debre then easily won the second and final round.

The National Assembly speaker is charged with ensuring the smooth running of the lower house and is the fourth highest ranked job in the French Republic after the president, prime minister and speaker of the Senate upper house of parliament.

Debre, 57, is the son of Charles de Gaulle's first prime minister, Michel Debre, and has been one of Chirac's closest confidants and most trusted political fixers since the 1970s.

He was previously parliamentary floor leader of Chirac's Gaullist Rally for the Republic (RPR) party that forms the core of the broader centre-right Union for the Presidential Majority (UMP) umbrella group created in April.

Chirac and his government have pledged economic and social reforms at the rate of one a month in the first year to combat scepticism with politics blamed by many for the brief resurgence of far-rightist Jean-Marie Le Pen in an April presidential vote.

An extraordinary session of parliament has been set for next month to present bills on crimefighting, justice reform and legislation to permit a quick five percent tax rebate this year as a foretaster of more ambitious tax-cutting pledges.

An investigating magistrate by profession, Debre has an unsmiling and occasionally abrasive manner and has proved effective in keeping party members in line.

His association with the president dates back to 1974, when Chirac, then agriculture minister, hired him as an aide. When Chirac went on to become interior minister and prime minister, Debre stayed on as an adviser.

Debre briefly quit politics before being named interior minister in the short-lived centre-right government of 1995-97 which was ousted from power when Chirac called early elections won by the left.