By Marja Novak

LJUBLJANA (Reuters) - Slovenia's finance minister Dusan Mramor resigned on Wednesday for what he said were personal reasons, prompting the opposition to call for an early election though junior members in the fragile ruling coalition insisted it was stable.

Prime Minister Miro Cerar said Alenka Smerkolj, Minister for European Cohesion, would fill in the role until a new finance minister had taken over, which he expected to happen in late August or early September. He did not name any candidates.

"In spite of this change the government will continue with its planned policy and will follow the strategy till 2020 which was laid out by minister Mramor and his team," Cerar said at a news conference to announce the resignation.

He would nominate a new candidate in the coming weeks, Cerar said. After that parliament must still give its approval.

Mramor, who tried to resign once before but was refused by Cerar, told the conference he had resigned "for entirely personal reasons".

Tanja Staric, a political analyst at Radio Slovenia, described the loss of Mramor as a blow to the coalition.

"With his resignation the chances that the government will survive till the end of its mandate (in 2018) are getting smaller," she said.

Junior coalition partners of the prime minister's Party of Modern Centre said the government remained stable in spite of Mramor's resignation.

But the opposition center-right New Slovenia Party called for an early election, saying the coalition is weak and not able to push through necessary reforms.

The coalition is struggling to reconcile demands for public sector wage and pension hikes with reducing the budget deficit.

Slovenia, which narrowly avoided an international bailout for its banks in 2013, managed to reduce its budget deficit to below the EU's ceiling of 3 percent of GDP last year after running excessive deficits for six years.

The government aims to reduce the deficit to 2.2 percent of GDP this year and then gradually bring it to zero by 2020.

Alta Invest chief economist Saso Stanovnik said further deficit reductions would depend largely on who became the new finance minister.

Analysts said the resignation could further delay the sale of the country's largest bank NLB, which was rescued by the state in 2013 and is due to be sold by the end of 2017.

Last week, Slovenia postponed investment roadshows for the sale due to market volatility caused by Britain's vote to leave the European Union.

(Editing by Raissa Kasolowsky)