* Malaysia says has sent team to Reunion Island
* French authorities say "ruling nothing out"
* Australia says number on debris could speed verification
* Currents could have pushed debris far from crash site - experts
* MH370 disappeared without a trace in March 2014 (Adds details about potential for U.S. lawsuits and damages limits)
By Joe Brock
SAINT-DENIS, Reunion, July 30 (Reuters) - Plane debris washed up on the French island of Reunion in the Indian Ocean is almost certainly part of a Boeing 777, a Malaysian official and aviation experts said, potentially providing some answers for families of those aboard last year's vanished flight MH370.
Malaysian investigators are due in Reunion on Friday and the object, identified by numerous aviation experts as part of a wing, is then due to be sent to a French military laboratory near Toulouse for checks, French police sources said.
National carrier Malaysia Airlines was operating a Boeing 777 on the ill-fated flight, which disappeared in March last year en route from Kuala Lumpur to Beijing in one of the most baffling mysteries in aviation history. It was carrying 239 passengers and crew.
The debris was found on Wednesday washed up on Reunion, a volcanic island of 850,000 people that is a full part of France known as an "overseas department", located in the Indian Ocean near Africa.
It is roughly 3,700 km (2,300 miles) away from the broad expanse of the southern Indian Ocean off Australia, where search efforts have focused, but Malaysian Prime Minister Najib Razak said currents could have carried wreckage that way.
"The location is consistent with the drift analysis provided to the Malaysian investigation team, which showed a route from the southern Indian Ocean to Africa."
Aviation experts who have seen widely circulated pictures of the debris said it may be a moving wing surface known as a flaperon, situated close to the fuselage.
"It is almost certain that the flaperon is from a Boeing 777 aircraft. Our chief investigator here told me this," Malaysian Deputy Transport Minister Abdul Aziz Kaprawi told Reuters.
There have been four serious accidents involving 777s in the 20 years since the widebody jet came into service. Only MH370 is thought to have crashed south of the equator.
"No hypothesis can be ruled out, including that it would come from a Boeing 777," the Reunion prefecture and the French Justice Ministry said in a joint statement.
Australia's Deputy Prime Minister Warren Truss said a number stamped on the 2 to 2.5 metres (6.5 to 8 foot) chunk of debris might speed up its verification.
"This kind of work is obviously going to take some time although the number may help to identify the aircraft parts, assuming that's what they are, much more quickly than might otherwise be the case," he said.
France 2 television showed a picture of the wing part with the figures "657 BB" stamped on its interior. That corresponds to a code in the 777 manual identifying it as a flaperon and telling workers to place it on the right wing, according to a copy of a Boeing document that appeared on aviation websites.
A source close to the French investigation said the plan was to transfer the wing flap to France's European mainland, along with a fragment of luggage that had also been found in the area.
"We're trying to get the debris of wing and the bag fragment sent off as soon as possible, if possible Friday, arriving probably on Saturday," said the source. The wing part would be sent to a military unit near Toulouse, while the luggage fragment may go to a police unit specialised in DNA tests.
Investigators believe someone may have deliberately switched off MH370's transponder before diverting it thousands of miles off course. Most of the passengers were Chinese. Beijing said it was following developments closely.
For the families of those on board, lingering uncertainty surrounding the fate of the plane has been agony. Some said the discovery of debris would still not solve the mystery.
"Even if we find out that this piece of debris belongs to MH370, there is no way to prove that our people were with that plane," said Jiang Hui, 41, whose father was on the flight.
Ghyslain Wattrelos, a French businessman whose wife and two children were on the missing flight, told French BFMTV the discovery of the debris had been "extremely painful".
"This doesn't give hope, this is a moment I have been fearing," he said. "As long as there wasn't any evidence of a crash, of wounded, of dead or whatever, there was a little glimmer of hope for us."
Zhang Qihuai, a lawyer representing some of the passengers' families, said a group of around 30 relatives had agreed they would proceed with a lawsuit against the airline if the debris was confirmed to be from MH370.
Daniel Rose, a partner at Kreindler & Kreindler LLP in New York, which is representing more than 50 victims' families, said the discovery is unlikely to trigger a wave of lawsuits.
Families are pursuing a settlement with insurer Allianz through Kreindler, he said, but the firm could sue before a two-year statute of limitations under the Montreal Convention, which governs such accidents, expires in March 2016.
Families want to sue in more favorable U.S. courts, a move that for most families would require arguing that an aircraft fault was at least partly to blame for the crash, he said.
"They're specifically not looking to have to file in China," Rose said. "They're much more interested in getting answers and the best place to do that is in the U.S."
One expert in psychology said the discovery could also give families a chance to grieve at last.
"If this is indeed debris from the jet, then it will provide families with much needed closure," said Nancy Smyth, dean of the University at Buffalo School of Social Work.
According to photographs, the piece of debris is fairly intact and with no burn marks or signs of impact. Flaperons help pilots control an aircraft while in flight. Boeing Co declined to comment on the photos.
Oceanographers said vast, rotating currents sweeping the southern Indian Ocean could have deposited wreckage from MH370 thousands of kilometres from where the plane is thought to have crashed.
If confirmed to be from MH370, experts will try to retrace the debris drift back to its source. But they caution that the discovery was unlikely to provide any more precise information about the aircraft's final resting place.
"This wreckage has been in the water - if it is MH370 - for well over a year so it could have moved so far that it's not going to be that helpful in pinpointing precisely where the aircraft is," Australia's Truss told reporters.
Robin Robertson, an oceanographer at the University of New South Wales in Sydney, said the timing and location of the debris made it "very plausible" that it came from MH370, given what was known about Indian Ocean currents. (Reporting by Tim Hepher, Emmanuel Jarry and Matthias Blamont in PARIS, Lincoln Feast and Swati Pandey in SYDNEY, Alwyn Scott in NEW YORK, Siva Govindasamy in SINGAPORE, Sui Lee Wee in BEIJING and Praveen Menon in KUALA LUMPUR; Writing by Dean Yates and Mark John; Editing by Peter Graff, Bill Rigby and Lisa Shumaker)