OSLO (Reuters) - Leaders of the four parties working to form a new government in Norway will continue to try resolve their differences until Wednesday and then go back to their boards for consultations, the Nordic country's likely next prime minister said on Monday.

"We are still not done. We have difficult issues, which we have not found solutions to yet," Erna Solberg, the leader of the Conservative party which wants to cut taxes and streamline government, told a news conference.

"We will continue talks until Wednesday, and then we will consult the party organizations," she said.

Two weeks after winning an election against the ruling centre-left, Solberg, 52, hopes to form a majority government with the populist right-wing Progress Party and two smaller centrist parties, the Christian Democrats and the Liberals.

All four have agreed that Solberg should become the new prime minister, but differ on issues such as opening new areas to oil drilling, immigration, environmental protection and spending of Norway's vast oil wealth.

The Conservatives cannot form a majority government without Progress and were expected to have to make concessions to the rightists without alienating the two other parties.

Progress wants to spend more of Norway's oil wealth and curb immigration. Although it has toned down its rhetoric to court respectability, some still see it as too radical for government.

The party came third in the September 9 poll.

Prime Minister Jens Stoltenberg, 54, is scheduled to step down after presenting a draft 2014 budget to the parliament on October 14, after having served two four-year terms in a row.

Norway has enjoyed rare economic success during the past decade, escaping Europe's economic crisis with little more than a scratch, as its booming offshore oil sector lifted per capita GDP to $100,000 and a huge public sector insulated the economy.

But growth is now slowing, competitiveness is stagnating, and the government's record on critical social services is mixed.

(Reporting by Nerijus Adomaitis; Editing by Sonya Hepinstall)