* Government expects oil prices to increase in 2010
* Oil to continue long-term down trend, gas sales seen up
* Oil/gas investment seen falling in 2010 vs 2009
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OSLO, Oct 13 (Reuters) - Norway expects oil prices to increase next year and sees the North Sea state's combined oil and gas output falling by 1.3 percent compared with 2009, the government projected in its 2010 draft budget.
Oil production, including natural gas liquids and condensate, was seen at 126 million cubic metres of oil equivalent (792 million barrels) next year, down from 133 million cubic metres this year. Gas production was seen up.
Including gas, output was seen at 233 million cubic metres of oil equivalent, down from 236 million in 2009. The budget saw output inching down to 230 million cubic metres in 2015.
"Whereas gas production is expected to increase by around 8 percent from 2008 to 2010, a decline in oil production of about 15 percent is expected in this period," the government said.
Total oil production, including natural gas liquids and condensate, is estimated at 2.3 million barrels per day in 2009, 7 percent less than in 2008, the energy ministry said.
While oil production is in decline as North Sea fields mature, gas production is set to rise to 103 billion standard cubic metres, an increase of about 7 percent compared to 2008.
Norway, which is not a member of the Organization of the Petroleum Exporting Countries (OPEC), is the world's No. 6 oil exporter and western Europe's biggest gas exporter.
The budget envisages the average price of Norwegian crude at 375 Norwegian crowns ($66.54) per barrel for 2009 and at 425 crowns next year. London Brent crude traded around $72 per barrel on Tuesday.
"With an improved economic outlook, oil demand is expected to grow into 2010," the energy ministry said in a statement.
"Together with continued constraints on OPEC production, this gives reasons to expect a tighter market balance and firmer oil prices next year," it added.
The budget said that investment in Norway's oil and gas fields would amount to some 118 billion crowns next year, still a relatively high level compared to recent years but down from 135 billion seen in 2009. The decline in investment, triggered by lower oil prices, could impact the offshore services sector.
"We still feel the effects from the financial crisis," Energy Minister Terje Riis-Johansen said in a statement. "The supply industry is reporting demanding conditions and lower rates of incoming orders. As a consequence, the government is working to secure a competitive supply industry, which contributes to industry development and employment."
Further details were not immediately available.
It said that 38 percent of a total of 13.4 billion standard cubic metres of recoverable resources off Norway have already been produced, with more than half of the oil gone and a little more than a fifth of the gas pumped out. (Reporting by Wojciech Moskwa, editing by Anthony Barker)