* Find may be in lower half of estimates in Lundin's licence
* Whole field seen holding 1.7-3.3 bln barrels
* Det norske may provide update on Feb. 15
* Lundin shares down 9.2 percent (Adds Det norske comment, share reaction, analyst)
By Balazs Koranyi and Joachim Dagenborg
OSLO, Feb 11 (Reuters) - The Johan Sverdrup oil field offshore Norway may contain less oil than previously expected, Swedish group Lundin Petroleum said, hitting the shares of firms with an interest.
Sverdrup, previously thought to contain up to 3.3 billion barrels of oil, is the biggest North Sea find in decades. Its operators - Lundin and Norwegian group Statoil have been drilling appraisal wells to narrow their estimates.
Lundin chief executive Ashley Heppenstall said on Monday the latest test drilling meant the "most likely mid-case for the Johan Sverdrup resources located in production licence 501 will be within the lower half of the previously guided 800-1,800 million barrels of oil equivalent range. We also believe that the resource calculation range remains wide."
The field lies in two licences with the half operated by Lundin estimated to hold between 800 million barrels and 1.8 billion while Statoil's half was seen holding between 900 million barrels and 1.5 billion.
Hopes have been high as an initial appraisal indicated the field may be in the upper part of estimates, while an additional find in the Geitungen prospect last year was seen adding to the resource.
Lundin shares were down 8.6 percent at 1230 GMT, while Norwegian group Det norske, a shareholder in the other licence that forms the field, fell 3.7 percent.
Statoil has said it expected to update the total reserve estimate in the fourth quarter this year, at the latest.
"They (Statoil) hesitate a little. We just have to wait and see what they say," Det norske CEO Erik Haugane said. "Information that is important to get out to the market is piling up. So, it is possible we also provide some numbers at our quarterly presentation. But you won't get the real numbers until Statoil comes out of the closet."
Det norske will publish quarterly figures on Feb. 15.
Statoil declined to comment.
Analysts said Lundin's comment meant market forecasts would be cut. "The most likely number for Lundin's licence is 1.0 billion to 1.1 billion barrels. But there is still considerable uncertainty," said Morten Lindbaeck, an analyst at Fondfinans.
"I interpret this as Statoil and the Norwegian Petroleum Directorate having told Lundin to be more sober (in their estimates)."
Arctic Securities analyst Trond Omdal said he had cut his estimate for the Lundin-operated side of the field to 1 billion of barrels of oil equivalent (boe) from 1.3 billion.
In the licence operated by Lundin, Statoil and Lundin each hold 40 percent while Danish company Maersk has 20 percent. In the licence operated by Statoil, state-holding firm Petoro holds a 30 percent stake, Det norske 20 percent, Lundin 10 percent, and Statoil 40 percent. (Additional reporting by Henrik Stolen; Writing by Victoria Klesty; Editing by Dan Lalor and Mark Potter)