No decision on final UK fighter numbers -officials

LONDON Oct 19 (Reuters) - Britain has not yet decided how many U.S. and European jet fighters it will ultimately order as a result of its defence review, officials said on Tuesday.

Prime Minister David Cameron confirmed in parliament that Britain would place an order for Lockheed Martin (LMT.N) F-35 Joint Strike Fighters, but did not specify a number of planes.

He said that by the 2020s, Britain's fast jet fleet would be built around the JSF and the four-nation Eurofighter Typhoon. The Typhoon is being built in three tranches with part of the final production run yet to be commissioned by buyer nations.

Officials briefing on the defence review said there had been no decision on how many JSFs and Typhoons would be ordered.

They said only 12 JSFs would be placed on the envisaged operational aircraft carrier, down from an initially planned 36.

One official said the final decision could be delayed until the next review expected to be carried out in 2015.

Britain has so far been expected to buy some 138 radar-avoiding JSF jets for the Royal Navy and Royal Air Force. The multinational JSF project is estimated to be worth $382 billion, making it the world's costliest arm programme.

(Reporting by Mohammed Abbas, Editing by Tim Hepher)