UPDATE 3-Norwegian oil minister quits, successor due Friday

(Adds details, comments from analyst)

By Aasa Christine Stoltz

OSLO, June 19 (Reuters) - Norway's Minister of Petroleum and Energy Aaslaug Haga resigned on Thursday from the centre-left government after reports of tax irregularities pressured her to quit, a move analysts said would have no effect on policy.

Haga, age 48, who became oil minister in the world's fifth biggest oil exporter and Europe's second biggest gas exporter in 2007, said she was resigning from the cabinet and stepping down as leader of the Centre Party for health reasons.

Prime Minister Jens Stoltenberg said the exit would not shake his three-party coalition that has governed since 2005 and faces an election next year. He said he will announce a successor from Haga's party on Friday.

"I have the following announcement -- Number 1, I resign as minister and, number 2, I resign as party leader," Haga told a news conference.

The oil and energy minister's job is one of the most important in Norway. The petroleum industry accounts for a quarter of gross domestic product, about 30 percent of state revenues and about half of total exports.

"This will not change anything in terms of government policy," said John Olaisen, an oil and gas analyst at brokers Carnegie in Oslo.

"The next big decision for the industry is whether to open for exploration the sea around the Lofoten islands and surrounding areas (in Norway's Arctic), and that is not expected until 2009-2010 -- in the next parliamentary term," he said.

With soaring energy prices and sagging production from maturing North Sea oilfields, the industry is lobbying hard to get access to potentially oil- and gas-rich exploration areas. The present government is wary of the environmental impact of exploration on the unspoiled Arctic region.

Haga has been a staunch supporter of Norway's push into renewable energy and has opposed opening up new swathes of the Arctic sea to oil and gas exploration.

"We will appoint the new energy minister tomorrow," Stoltenberg told a news conference, adding that her replacement will come from the Centre Party, which represents rural and regional interests.

Stoltenberg said the coalition of his Labour Party, the Centre Party and Socialist Left did not depend on individuals and would continue to carry out the policy platform adopted after elections in 2005. "We will continue our cooperation."

Haga, referring to media headlines about unpaid taxes on a rental property owned by her and her husband, acknowledged that she may have made a mistake, but said she did not know about it.

"There may have been a mistake. If we have erred, I can assure you that this will be cleared up," she said.

Haga, who became party leader in 2003 and helped form the "Red-Green" coalition government led by Stoltenberg in 2005, said her resignation was not political, but a personal decision with a view to her health.

"I do not want to jeopardise my health. It cannot survive this life any longer," she said.

Stoltenberg said he respected her decision to quit and that he was assured that all the facts would be "put on the table."

He praised her work in the government and said she had achieved "big and important results."

(Additional reporting by John Acher and Wojciech Moskwa)