* Planemakers COMAC, UAC show model of widebody jet at expo

* 50-50 Shanghai-based JV to begin operations this year

* Jet targets market dominated by Airbus, Boeing

* State-backed plan seen highly ambitious by analysts (Adds executive comments, background details)

By Brenda Goh

ZHUHAI, China, Nov 2 (Reuters) - China and Russia on Wednesday offered a glimpse of a grand plan to jointly make a jumbo jet to rival giants Boeing and Airbus, showing a model of the unnamed plane to be developed by a joint venture that will start work this year.

State-owned planemakers Commercial Aircraft Corporation of China (COMAC) and United Aircraft Corp (UAC) of Russia said they have started the hunt to find suppliers as they presented the mock-up of the widebody jet for the first time in public at a ceremony during Airshow China, the country's biggest air expo.

But executives of both firms at the event offered no concrete details on financing and few technical specifications for a project that Western analysts have said is highly ambitious, difficult to pull off and likely to carry a high price.

Guo Bozhi, general manager of COMAC's widebody department, said a 50-50 joint venture based in Shanghai will start operations this year. First announced in 2014, the project has been kept largely secret, though the firms have said they want conduct a maiden flight in 2022 and begin deliveries in 2025 - targets Western industry analysts consider unlikely, saying widebody jets can take decades rather than years to develop.

"A widebody jet is an extremely complicated product, which will require a lot of skills (to develop) and require broad industrial knowledge," Guo told reporters. "China and Russia each have their own advantages."

Descriptions accompanying the model showed the firms ultimately envision three variants of the aircraft, based on a basic version that will hold 280 seats with a range of up to 12,000 kilometres.

The decision to base the venture in Shanghai was a "mutual decision" Guo said at the event, attended by COMAC Chairman Jin Zhuanglong, UAC's Chief Executive Yury Slyusar as well as Russia's Minister of Trade and Industry Denis Manturov. Guo declined to say how much each party had invested in the project.

A global effort to search for and assess potential suppliers is now under way, said COMAC, which is separately occupied with pushing its own C919 narrow-body passenger jet towards a long-delayed maiden flight, now aimed for the end of 2016 or early 2017.

U.S. firms Honeywell and United Technologies Corporation said on Wednesday they discussed the China-Russia jet with COMAC officials at the airshow, without commenting on the nature nor the subject of the contacts.

"We will choose suppliers who have rich experience in development, whose products are competitive globally, and who can continually guarantee quality from the development stage until the planes go into operation," Guo said.

Though a 50-50 JV, analysts view the Chinese side as being the more influential in the project.

The firm's Shanghai headquarters tells "where the balance of power is going to be and that reflects the size of the Chinese domestic market," said Sash Tusa, analyst at London-based consultancy Agency Partners.

"The volumes for a widebody jet are far smaller than for a narrow body...so I think suppliers are going to be much more careful about this than for the (COMAC) C919," he said.

(Reporting by Brenda Goh; Editing by Kenneth Maxwell)