Argentina's Massa in line for key Congress role on Fernandez presidential ticket

BUENOS AIRES (Reuters) - Argentine politician Sergio Massa, who recently pledged his support to the main opposition challengers to President Mauricio Macri, is in line to play a key role in the country's Congress if his new allies win national elections later this year.

The former chief of staff said on Tuesday he would be the first on a list of candidates to lead the Chamber of Deputies, one of the country's two houses of Congress, if Peronist hopeful Alberto Fernandez wins the presidency.

Massa, a centrist politician who had himself eyed a presidential run, struck an alliance last week with Fernandez and his unrelated running mate Cristina Fernandez de Kirchner, who served as president from 2007 to 2015.

The alliance - which had raised the question of what role Massa would take - is expected to widen the appeal of the Fernandez-Fernandez ticket to more moderate voters, particularly in the key province of Buenos Aires.

Argentina's National Congress is comprised of the Senate and the Chamber of Deputies.

"Beyond my personal interest, our biggest responsibility is to give Argentines the possibility to build a majority to have a new government," Massa said during a seminar in Buenos Aires.

The Fernandez-Fernandez pairing will take on center-right leader Macri in elections in October. If no candidate wins 45% of votes in the first round of voting - or wins at least 40% with a 10 percentage point margin over the second-place finisher - the race will go to a runoff in November.

Macri, who has been hit hard in the polls by a painful economic recession and market volatility, will seek re-election with running mate Miguel Ángel Pichetto, another moderate Peronist.

(Reporting by Gabriel Burin; writing by Adam Jourdan; editing by Leslie Adler)