Norway picks U.S. combat jet over Swedish rival

* Deal for 48 planes worth around $2.54 bln

* Chose Lockheed Martin's F-35 Joint Strike Fighter

* Rejected Saab's Gripen

* Deal biggest defence investment in Norway's history

* Lockheed stock up 1.2 pct, Saab closes down 12 pct

(Adds details, comments from news conference)

By Aasa Christine Stoltz and John Acher

OSLO (Reuters) - Norway will buy 48 of Lockheed Martin's (LMT.N) F-35 Joint Strike Fighters, in a deal worth about $2.54 billion, instead of Swedish Saab's (SAABb.ST) Gripen to replace its ageing F-16 warplanes.

The deal is the biggest defence investment in NATO member Norway's history, and the government said that total costs over the lifetime of the aircraft are estimated at 145 billion Norwegian crowns ($20.43 billion).  Continued...