* Norway's gas exports cut by 17 pct on Thurs vs Wed
* UK gas prices rise on the news
* Gas exports cut to last until 0500 GMT on Friday
* Statoil's gas output cut by 25.5 mcm/day on Thursday
By Balazs Koranyi and Gwladys Fouche
OSLO, Nov 28 (Reuters) - Norwegian gas exports were cut by afifth of peak capacity on Thursday after an outage at the plantprocessing gas from Royal Dutch Shell's giant OrmenLange field, limiting gas exports to Europe at a time of highdemand.
Norway is Britain's top gas supplier and the EuropeanUnion's second-largest gas supplier after Russia, supplying 20percent of its gas.
British gas prices rose, with prices for delivery within theday trading at 71.45 pence per therm at 0930 GMT on Thursday, up1.52 pence since opening.
Prices for delivery on Friday were up 0.55 pence to 70.75pence a therm.
At 0939 GMT Norwegian gas exports were flowing at 251 mcmper day, 52 mcm per day less than on Wednesday and equivalent toa 17 percent cut, according to data from Thomson Reuters PointCarbon.
Norwegian exports are currently 21.5 percent below Norway'scurrent peak capacity of 320 mcm per day.
Production at the Ormen Lange onshore plant halted late onWednesday after a power trip. North Sea infrastructure operatorGassco said the outage would cut Norwegian gas exports by 35 mcmper day from 0500 GMT on Thursday until 0500 GMT on Friday.
It increased that figure to 45 mcm per day at 0910 GMT.
Separately, Statoil said on its website its gas exportswould be cut by 25.5 mcm per day on Thursday, up from the 13 mcmper day announced earlier in the day.
Its gas output would also be reduced by 8.5 mcm per day onFriday.
It did not give a reason for the outage, but it is likelythat it is due to the problems at Ormen Lange. The dates for theoutages coincide and Statoil has a stake in the field.
Statoil also sells gas on behalf of Norwegian state-ownedfirm Petoro, which also has a stake in Ormen Lange.
The other partners in Ormen Lange are Denmark's DONG Energy and ExxonMobil.
