HELSINKI (Reuters) - The first prominent politician to bid for the leadership of Finland’s eurosceptic party promised on Monday to maintain its moderate line, setting up a contest with a rival whose more hardline stance could break up the government.

Finland's co-ruling Finns party politician Sampo Terho speaks during a news conference in Helsinki, Finland March 6, 2017 REUTERS/Tuomas Forsell

Parliamentarian Sampo Terho is a close ally of Timo Soini, the foreign minister who is stepping down in June from the helm of The Finns after 20 years, steering it into government as a coalition partner in 2015.

“The party is entering a new phase ... but values behind our policy will remain similar,” Terho told a news conference, announcing his decision to run for the party leadership.

He is likely to face off against Jussi Halla-aho, a member of the European Parliament who has a much tougher stance against immigration and Finland’s membership of the EU - a position that could break up the delicately balanced three-party government.

“I am a critic of immigration too. But I consider myself moderate,” Terho said. “I have a broad agenda on political issues.”

In recent years, The Finns has softened its nationalist and anti-EU platform and distanced itself from rising far-right parties across Europe - a choice that helped it enter the coalition government in 2015.

But that stance - which has included public spending cuts, backing the EU bailout for Greece and providing help for migrants - has angered some of its core voters, and the party, the second-biggest in parliament, now ranks fifth in the polls with support of about 9 percent of Finns.

While Halla-aho - who commands the same amount of support within the party as Terho, according to a poll by Lannen Media in January - has bluntly said Finland would be better off outside the EU, Terho on Monday repeated his vague support for a possible “Fixit” referendum if the idea gets wide backing in the party.

Terho told reporters he still backed the austerity drive which has provoked strikes and demonstrations against the centre-right government.

In 2012, Halla-aho was fined by the Supreme Court for blog comments which linked Islam to pedophilia and Somalis to theft. But that did not put off his supporters and he received the second most votes of any Finnish politician in the 2014 European election.

“Halla-aho is the only candidate who can connect the Finns party to the wider European right-wing-populist movement ... this is what people want right now,” said Sebastian Tynkkynen, a former Finns vice-chairman who wants the party to quit the government. “Halla-aho will be a clear winner.”

Kimmo Gronlund, political science professor at Abo Akademi, said Halla-aho would pull The Finns sharply to the right.

“In the hands of Halla-aho, the party would marginalize and radicalize, and draw similarities to Sweden Democrats,” he said, referring to the anti-immigration party across the border that has so far been spurned by the mainstream despite a surge in polls to a support of 17.5 percent.

Halla-aho, who has said he will likely seek the leadership, is yet to confirm his candidacy for the party congress vote, due in June.