FARNBOROUGH, England (Reuters) - Belgium is being offered a possible role in future European combat jet developments if it picks the Eurofighter Typhoon over the U.S.-built F-35, in a fierce contest to rearm the country’s air force, a senior official with Britain’s BAE Systems said.

British Eurofighter Typhoons are viewed from a U.S Air Force KC-135 during a European Tanker Symposium from RAF Mildenhall, Britain May 17, 2018. REUTERS/Darren Staples - RC12EE7F8720

The sweetener comes as four nations behind the Eurofighter - Britain, Germany, Italy and Spain - step up lobbying to try to secure the order for 34 multi-role jets, amid reports that the Lockheed Martin LMT.N F-35 is viewed as the leading contender.

Competition for arms sales is heating up across Europe, with fighter jet tenders open or starting soon in Belgium, Switzerland, Germany, Finland and Poland.

The Belgian government is expected to pick a winner in its fiercely contested tender by October. France opted out of the formal competition, but has pitched Dassault Aviation's Rafale AVMD.PA as part of a larger military cooperation deal.

Anthony Gregory, BAE’s campaign director in Belgium, told Reuters at the Farnborough Airshow that his company was offering direct investments in Belgian firms to ensure they were ready to participate in a future fighter program.

That proposal could appeal to Belgium, whose officials have expressed regret that they skipped becoming a partner in the F-35 program when it first began in the 2000s.

“They’re on the outside now, and as they look to the future, they would want to be more of a partner in whatever program comes beyond this particular replacement,” he said. “Our offer invests in Belgian industry as part of that bigger picture.”

Lockheed has also offered orders for Belgian industry as part of its F-35 bid. U.S. officials argue that picking the F-35 would give it a role on the world’s most advanced fighter jet, joining Britain, Italy, Norway, Denmark, the Netherlands and Turkey, which are also ordering the F-35 jets.

Eurofighter’s sales chief Peter Maute said he expected to sell “several hundred” more aircraft in coming years, given rising military spending and ongoing competitions.

The Eurofighter consortium comprises Airbus AIR.PA, Britain's BAE Systems BAES.L and Italy's Leonardo LDOF.MI.

Maute said the Eurofighter nations had mounted an unusually concerted lobbying effort at the company’s urging.

Defense and trade ministers from those countries have sent separate letters to the Belgian government, Gregory said, arguing that choosing a European-built jet would deepen European defense cooperation and advance a key European Union goal.

Eurofighter Jagdflugzeug CEO Volker Paltzo told reporters the company was in discussions with the core nations about further enhancements to the aircraft’s cockpit and engines, which could later be transferred to future fighter programs.

He said he expected a newly unveiled British future fighter project and a rival Franco-German program would eventually converge into one joint European venture, echoing comments by Airbus Defense and Space Chief Executive Dirk Hoke and Leonardo CEO Alessandro Profumo.