PARIS (REUTERS) - Big finance waded into a rain-soaked Paris Airshow with more than US$10 billion (S$12.5 billion) in orders for jumbo passenger jets as planemakers duelled over strategy for large aircraft on Monday.

The world's biggest aircraft lessor, a unit of General Electric, became the second buyer to endorse a larger version of Boeing's 787 Dreamliner, weeks after the lightweight jet went back into service after a three-month grounding.

Confirming a Reuters report, the GECAS subsidiary said it would sign up for 10 of the stretched 787-10 passenger planes, joining a US$30 billion order haul that industry sources say Boeing is assembling to formally launch the jet on Tuesday.

An influential German leasing company, Doric Asset Finance, little known outside the specialist world of aviation financing, also splashed out on 20 Airbus A380 superjumbos worth US$8 billion at list prices to anticipate rising demand.

Total orders on day one of the world's largest aerospace event swelled to more than US$30 billion in three hours as heavy rain lashed the Le Bourget pavilions.

But, despite the early flurry, the number of orders this year was expected to be down on the last Paris show in 2011, GECAS chief executive Norman Liu told reporters.

"It is shifting to more of a wide-body story," he said, referring to long-haul jets seating anywhere from 200 people on small wide-bodies to 525 on the double-decker A380.

Doric, which is already involved in financing A380 jets for Emirates airline, the aircraft's largest operator, said its deal would be finalised in months, with deliveries to start in 2016.

"We see how airlines that do not yet have the A380 are interested in it and approach us and ask questions, which shows us that there is pent-up demand for this aircraft," Mr Mark Lapidus, chief executive of Doric Lease Corp, said.

"If anything, we are perhaps under-ordering the A380."

It remained unclear whether Doric had already identified the eventual customers to whom it would rent out the planes.

Lessors have until now been reluctant to back the A380 because it is highly customised and expensive to convert.

The move is a boost for Europe's Airbus which has struggled to sell the model in the past year haunted by wing cracks, and had recorded no sales so far in 2013.

Boeing says airlines do not want to invest heavily in the largest jets above 400 seats, even though it originally defined the category with its 747, and would prefer to buy smaller planes built with new weight-saving materials.

Airbus has stood by the industry mammoth, saying urbanisation and airport congestion will drive traffic towards planes that can keep pace with demand for travel between hubs.

Most attention at the air show, however, focused on a new generation of mid-sized long-range jets, seen as crucial to the future of both companies and their suppliers.

Boeing said last week it sees a US$1 trillion market over the next 20 years for mid-sized, twin-engined passenger jets, a category that includes its carbon-composite 787 Dreamliner.

Days after it surprised the industry by making the first flight of its rival A350 before the show, Airbus will attempt a curtain call on Friday with a fly-by for French President Francois Hollande, on only the plane's third test.

Airbus and its US rival have placed bets worth tens of billions of dollars on the success of this market.

Behind them Canada's Bombardier Inc is betting the same technology will be suitable for smaller planes as it seeks to boost orders for its new CSeries, due to fly this month.

For Boeing, the latest addition to its fleet, the 323-seat 787-10, is partly designed to serve dense routes within Asia - a region fast emerging as the world's largest travel market.

The company claims it will have the best economics of its kind, while Airbus sees it as a repeat of a previous 767 flop.

Singapore Airlines, British Airways and Air Lease Corp are expected to place orders for the 787-10. They will be joined by United Airlines, industry sources said.

Boeing re-introduced the 787 Dreamliner to service in April after a three-month grounding due to battery problems. Now it is also looking at a partial redesign of its 777 mini-jumbo too.

Leasing companies and airlines, looking beyond the financial crisis, meanwhile, placed orders for more than US$20 billion small narrow-body planes like the Boeing 737 MAX and the A320neo.

Lufthansa confirmed a US$10 billion order for 100 Airbuses and lessor ILFC signed up for US$5 billion, and Boeing got a finalised order worth US$6 billion from Britain's TUI Travel.

The military side of the world's largest aerospace event was muted by comparison with previous years.

US arms firms have scaled back but all eyes will be on the return of Russian fighters, noted for dramatic stunt displays.

Budget cuts prevented the US government from bringing F-16 jets, which usually show off their skills during the air show.

Lockheed Martin Corp, maker of the F-16 and F-35 fighter jets, did not bring even the mock-up model of the F-35, the Pentagon's largest programme which faces concerns about costs.