VIENNA (Reuters) - Austria's far-right Freedom Party lost ground on Sunday at a third consecutive state election, further clouding its prospects for joining a national coalition after parliamentary elections due by September.

Heinz-Christian Strache's Freedom Party - which had stumbled badly in two other state votes this year, including in its heartland of Carinthia - fell below 10 percent in the western province of Tyrol, provisional results showed.

In more good news for the centrist coalition in Vienna, Eurosceptic billionaire Frank Stronach's new party failed to clear the minimum vote hurdle, halting its momentum from the two previous state elections at which it won 10 percent.

Team Stronach national parliamentary leader Robert Lugar blamed party infighting for the poor showing in Tyrol, saying: "We will do better in the national elections."

Partners in the federal coalition - the conservative People's Party and center-left Social Democrats - slipped to their worst post-war results in the state but still finished first and second in a fragmented field of 11 parties.

The People's Party fell below 40 percent but still took first place in Tyrol where it has long dominated, lending some support to national leader and Deputy Chancellor Michael Spindelegger.

Chancellor Werner Faymann's Social Democrats fell below 14 percent for second place.

National polls show the coalition parties comfortably ahead, with the Social Democrats on around 27 percent and the People's Party on 25 percent. Freedom stands at 19 percent, while Team Stronach gets 10 percent and the Greens 13 percent.

State elections in Salzburg, which has been shaken by a financial scandal, take place next Sunday in the last regional test before the national parliamentary vote.

(Reporting by Michael Shields; Editing by Robin Pomeroy)