Czech Prime Minister Petr Necas said on Wednesday he would seek early elections in June if he cannot quickly regain a clear parliamentary majority after a junior coalition party split, a potential death blow to his fragile centre-right coalition.

Tuesday's defection by Deputy Prime Minister Karolina Peake and her allies from the centrist Public Affairs party weakened Necas's support in parliament and it remained unclear whether he could still command enough votes to avoid a government collapse.

Peake, whose argument was with her scandal-ridden party rather than Necas's government, retains her cabinet position and said her faction would continue to back the coalition.

But the rest of the Public Affairs party will no longer be part of what was a three-party coalition which only last week agreed new deficit-cutting measures.

If I do not have clear knowledge by Monday that the government has a safe majority, the proper solution will be to call an election in June, Necas told reporters.

An early election would likely bring the centre-left opposition Social Democrats to power while Public Affairs would drop out of parliament entirely.

An opinion poll showed on Wednesday the Social Democrats would win 37 percent of the vote, versus 17.5 percent for Necas' Civic Democrats and 11.5 percent for his main ally, the conservative TOP09. Public Affairs - even before the split - would get just 2 percent, not enough to win any seats.

While most analysts predicted Peake would bring enough deputies with her to support the cabinet, the head of the TOP09 parliamentary faction was sceptical.

My opinion is that this will probably lead to the dissolution of parliament, Petr Gazdik told Czech Television.

DISTRUSTED

Social Democrat leader Bohuslav Sobotka called for an election as soon as possible.

It is clear that a government weakened like this, which is distrusted by 80 percent of the people, has lost the authorisation to make fundamental reforms, he said.

Only last week, the three coalition party leaders agreed on tax hikes and budget savings for 2013-14, bridging a policy rift that had threatened to topple the government less than halfway into its four-year term.

The agreement to cut the budget deficit to below 3 percent of gross domestic product next year confirmed the central European country's focus on fiscal austerity, which has hurt growth but won it confidence in financial markets.

The time lost by the possible dissolution of parliament and forming a government after the early election would put pressure on the next administration to push any savings measures through.

Public Affairs was the unstable element in the coalition since it was formed after the 2010 election on a platform of tight budgets and savings in the pension and welfare systems.

The party has been hit by scandals involving its most influential leader, Vit Barta, who was given an 18-month suspended sentence last week for bribing party colleagues to keep their loyalty.

Barta, a party rival of Peake, appealed against the verdict and left the party's parliamentary faction, but retained his behind-the-scenes influence.

Necas said he could no longer cooperate with the faction led by Barta, a wealthy businessman who is viewed with suspicion by coalition partners due to his former ownership of a detective agency that, among other work, followed politicians in the past.

Without Public Affairs, the two remaining government parties can rely on 92-93 seats in the 200-seat lower house, so they would need at least eight or nine of Public Affairs' 21 deputies to join the Peake faction to secure a majority. They could also rely on a couple of independents.

Czech media reported six deputies had already declared allegiance to Peake, a trained lawyer in charge of anti-graft policy, but some have pledged loyalty to the Barta wing.

(Editing by Robin Pomeroy)