* Cuts delayed to Oct 2016
* Investors fearing lost revenues considering legal action
* Two additional small pipeline areas get exemption (Adds detail, investor reaction)
OSLO, June 27 (Reuters) - Norway postponed a planned cut in natural gas pipeline tariffs by three years on Thursday but failed to appease angry international investors who oppose the cuts and say they will consider legal action.
Cuts to tariffs which pipeline owners charge for using the lines will now take effect in October 2016, said the oil and energy ministry, which hopes lowering costs for users will spur them to invest more in smaller fields and exploration of new reserves in the Arctic.
"Lower costs for gas transport will strengthen the competitiveness of Norwegian gas. At the same time the owners (of the pipeline system) are getting reasonable profits," Oil and Energy Minister Ola Borten Moe said in a statement.
Some of those owners have said the move will cost them 6.6 billion dollars in lost earnings over the next two decades and are weighing legal action.
"This is not giving us a reasonable return," said Knud Noerve, chief executive of Infragas, owned by Canada's PSP Investments, adding the move would make Norway a less attractive investment target.
"We are very disappointed that they have gone (ahead) in reducing the tariffs. We will now look at all options, including legal action," said Trygve Pedersen, chief executive of Solveig Gas, owned by Canada's PSP Investments, the Abu Dhabi Investment Authority and Allianz.
International investors including the Abu Dhabi Investment Authority, German insurer Allianz, Swiss bank UBS, Canada's PSP Investments and France's Caisse des Depots have spent more than $5 billion in recent years acquiring stakes in Norwegian pipelines.
The tariffs are based on a formula that includes capital and operating costs. Oslo plans a 90-percent reduction in the capital element of the tariffs.
The ministry said, however, that the small Kvitebjoern and Norne lines would be exempted from the cuts, bringing the number of exempted pipeline areas to four.
But cuts will go ahead on the other five areas which form the bulk of Norway's 8,000-kilometre-long network transporting gas to Britain, France, Belgium and Germany.
Norway overtook Russia last year to become the European Union's biggest gas supplier, delivering 106 billion cubic metres of gas.
($1 = 6.0998 Norwegian kroner) (Reporting by Gwladys Fouche and Balazs Koranyi, editing by Jason Neely)