(Adds reaction from Airbus and Boeing)
By Andrea Shalal
BERLIN, Jan 31 (Reuters) - Germany will pick either the Eurofighter or Boeing's F/A-18 fighter jet to replace its Tornado warplanes, knocking Lockheed Martin's F-35 stealth fighter out of a tender worth billions of euros, Defence Ministry sources said on Thursday.
The ministry will make a final decision after receiving detailed information from Boeing and Airbus about the aircraft, which must be able to carry U.S. nuclear weapons to fulfil Germany's obligations to NATO, the sources said.
No timetable for a decision was given, but the process could take time since the U.S. government will have to certify both jets to carry the nuclear weapons. Germany has 85 operational Tornado jets, but not all are equipped to carry nuclear weapons.
The German air force will also move ahead with long-awaited plans to replace its 33 oldest Eurofighter jets, now used mainly for air policing or training, with new, more capable Eurofighters in coming years, the sources said.
That will translate into orders worth up to 3 billion euros ($3.4 billion) for Airbus, according to sources familiar with the issue.
In marketing the F/A-18, Boeing had underscored its high readiness rates, relatively low cost and strong electronic attack capabilities, arguments that resonated in military circles.
The decision marks a big setback for Lockheed, the top U.S. arms maker, which had hoped to add to recent F-35 sales to other European countries, including Belgium.
Germany's air force chief of staff was fired last year after he expressed a clear preference for the F-35. The ministry later said it favoured a "European solution".
Airbus welcomed the news about the Eurofighter replacement purchases, and said it remained convinced that its jet offered the lowest-risk prospect for replacing the Tornado jets.
Lockheed said it had not been officially notified of a German decision. It said the F-35 offered the most capability, lowest life-cycle cost of any fighter on the market, and long-term industrial and economic opportunities.
Boeing declined to comment, as did the U.S. embassy in Berlin.
Germany's Social Democrats (SPD), junior partners in Chancellor Angela Merkel's ruling coalition, had argued against rushing into any decision to buy U.S. aircraft and demanded closer study.
Defence Minister Ursula von der Leyen, a conservative, had promised a decision on the procurement plans by the end of 2018, but her ministry became mired in scandals over the use of outside consultants and other issues.
Military officials argue that the Tornadoes, which entered service in 1983, need urgent replacement due to rising maintenance costs. Sources familiar with the matter say it could cost around 8 billion euros to keep the planes flying past 2030.
Sources familiar with the process last year had said the ministry wanted to split the order between one of the two U.S. planes and the Eurofighter, which is built by Airbus, Britain's BAE Systems and Italy's Leonardo SpA. But it now appears Berlin will pick just one winner.
Paris, Germany's closest European partner, had warned that buying the F-35 in particular could derail plans to develop a new Franco-German fighter by 2040. ($1 = 0.8732 euros) (Reporting by Andrea Shalal; editing by Thomas Escritt and Kevin Liffey)