* Search area widens to take into account French satellite images
* Weather conditions forecast to deteriorate
* Chinese, Japanese aircraft joining international search team
* NASA also says joining search effort
By Matt Siegel and Niluksi Koswanage
PERTH/KUALA LUMPUR, March 24 (Reuters) - The search area for a missing Malaysian jetliner in remote seas off Australia was widened on Monday after French satellite images revealed potential "floating debris" several hundred kilometres north of pictures previously captured by U.S. and Chinese satellites.
Australian Deputy Prime Minister Warren Truss said the new lead in the hunt for Malaysia Airlines Flight MH370 was promising, but cautioned that the search in the icy southern Indian Ocean remained difficult.
"It's a lot of water to look for just perhaps a tiny object," Truss told ABC Radio. "Today we expect the weather to deteriorate and the forecast ahead is not that good so it's going to be a challenge, but we will stick at it."
Truss said the object spotted by a French satellite, which was reported to Malaysia on Sunday, was 850 km (528 miles) north of the current search areas for the Boeing 777 that vanished on March 8 with 239 people on board.
"That's not in the area that had been identified as the most likely place where the aircraft had entered the sea," Truss said.
Australia had used a U.S. satellite image of two floating objects to frame a search area some 2,500 km (1,430 miles) southwest of Perth.
Flight MH370 vanished from civilian radar screens less than an hour after taking off from Kuala Lumpur on a scheduled flight to Beijing. Most of the passengers were Chinese.
A total of 10 planes, including Chinese military Ilyushin IL-76 and Japanese P-3C aircraft joining the search for the first time, are due to sweep a 68,000 sq km area on Monday.
The crews are zeroing in on the areas around where the earlier sightings were made in an effort to find the object identified by China and other small debris, including a wooden pallet, spotted by a search plane on Saturday.
China said the object it had seen on the satellite image was 22 metres long (74ft) and 13 metres (43ft) wide.
It could not easily be determined from the blurred images whether the objects were the same as those detected by Australia, but the Chinese photograph could depict a cluster of smaller objects, said a senior military officer from one of the 26 nations involved in the search.
The wing of a Boeing 777-200ER is approximately 27 metres long and 14 metres wide at its base, according to estimates derived from publicly available scale drawings. Its fuselage is 63.7 metres long by 6.2 metres wide.
NASA said it would use high-resolution cameras aboard satellites and the International Space Station to look for possible crash sites in the Indian Ocean. The U.S. space agency is also mining archived images collected by instruments on its Terra and Aqua environmental satellites, said NASA spokesman Allard Beutel.
"Our satellites and space-based cameras are designed for long-term scientific data gathering and Earth observation. They're really not meant to look for a missing aircraft, and obviously NASA isn't a lead agency in this effort. But we're trying to support the search, if possible," Beutel said.
Truss said the aircraft flying on Monday would be focused on searching by sight, rather than radar, which can be tricky to use because of the high seas and wind in the area. Civil aircraft, which can carry more people, have joined the search.
Truss warned that the search could be hampered further by a cyclone in the northern Indian Ocean.
"Clearly it won't be cyclonic when it gets down into the southern waters where we are dealing with this search, but certainly it could stir up less favourable weather ... and looking visibly for debris or anything of interest is the best chance of success," he said.
HIJACK OR SABOTAGE?
Investigators believe someone on the flight shut off the plane's communications systems, and partial military radar tracking showed it turning west and re-crossing the Malay Peninsula, apparently under the control of a skilled pilot.
That has led them to focus on hijacking or sabotage, but investigators have not ruled out technical problems. Faint electronic "pings" detected by a commercial satellite suggested it flew for another six hours or so, but could do no better than place its final signal on one of two vast arcs.
The lack of solid news has meant a prolonged and harrowing wait for families of the passengers, who have complained both in Beijing and Kuala Lumpur about the absence of information, many breaking down with grief.
A Malaysian statement said a "high-level" team briefed relatives in Beijing on Sunday in a meeting that lasted more than six hours.
While the southern arc is now the main focus of the search, Malaysia says efforts will continue in both corridors until confirmed debris is found.
"We still don't even know for certain if the aircraft is in this area," Truss said of the southern Indian Ocean search. "We're just clutching at whatever little piece of information that comes along to try to find the place we can concentrate the efforts." (Additional reporting by Irene Klotz. Writing by Jane Wardell. Editing by Dean Yates)