* Brazil government says debris is from Air France flight

* All 228 people aboard thought to be dead

* Race against time to find flight data, voice recorders (Recasts, adds quotes; new throughout)

By Pedro Fonseca and Maria Pia Palermo

RIO DE JANEIRO, June 2 (Reuters) - Brazilian military planes found wreckage on Tuesday from an Air France jet that crashed in the Atlantic Ocean with 228 people aboard, the airline's worst disaster in its 75-year history.

Brazilian Defense Minister Nelson Jobim said there was "no doubt" that a 5-km (3-mile) strip of debris in the high seas was from the Airbus A330 that went missing in stormy weather early on Monday. Experts were certain that all aboard died.

"The remains, the wreckage, are from the Air France plane," a somber Jobim said at a news conference in Rio de Janeiro, where the plane took off for Paris on Sunday night.

Distraught relatives who had been praying for a miracle said they had given up. [ID:nN02520837]

"The last bit of hope that we had no longer exists ... Before a lot of us were hoping that the plane could have landed on an island or something like that, but no more," said Aldair Gomes, whose son was on the plane.

Airplane seats, an orange buoy, wiring, pieces of metal and fuel stains were spotted in the water by Brazilian air force pilots about 1,200 km (745 miles) northeast of the coastal city of Recife.

So far no bodies have been sighted, and pulling out bits of wreckage may not start until Wednesday when navy ships with divers arrive.

It is likely to be extremely difficult to find the flight data and voice recorders that hold clues to why the plane fell out of the sky in the middle of the night. The recorders could be on the ocean floor at a depth of 2,000 to 3,000 meters (6,600-9,800 feet), Jobim said.

Brazilian President Luiz Inacio Lula da Silva said he was confident that the black boxes would be found.

"I think a country that can find oil 6,000 meters under the ocean can find a plane 2,000 meters down," he told reporters in Guatemala, referring to recent oil finds by Brazil's state energy company in ultra-deep waters.

The recorders are designed to send homing signals for up to 30 days when they hit water, but many do not float well. It could be among the hardest recovery tasks since the exploration of the Titanic, one expert said.

"If you think how long it took to find the Titanic and that the debris would be smaller, you are looking for a needle in haystack," said Derek Clarke, joint managing director of Aberdeen-based Divex, which designs and builds military and commercial diving equipment. [ID:nL2690712]

MYSTERY, RELATIVES WANT ANSWERS

Authorities were baffled by how a storm could have caused the modern plane operated by three experienced pilots to crash without sending a mayday call. [ID:nL2721255]

Experts from France have arrived in Brazil to lead the investigation with help from Brazilian teams.

Brazil's air force last had contact with Flight AF 447 at 0133 GMT on Monday when it was 565 km (350 miles) from its coast. The last automated signals, which reported an electrical failure, were received about 40 minutes later.

One theory is that a lightning strike or brutal weather set off a series of failures. But lightning routinely hits planes and could not alone explain the downing, aviation experts said. [ID:nL1719357]

Two Lufthansa jets believed to have been in the same area half an hour before the Air France mishap are expected to provide clues for investigators, the World Meteorological Organization said. [ID:nL21026278]

Among the 216 passengers were executives from major companies that have ramped up investments in Brazil in recent years and European tourists returning from its famous beaches as well as seven children and one baby.

"My son died on his birthday," said a tearful Diana Raquel, mother of British-based Brazilian dentist Jose Rommel Amorim, who turned 35 on Sunday.

French electrical equipment firm CGED said 10 of its staff were on the plane with their partners after visiting Brazil, which declared three days of mourning. (Additional reporting by Brian Ellsworth, Alonso Soto, and Rodrigo Viga Gaier in Rio; Fernando Exman in Brasilia; William Maclean and Jason Neely in London; Tim Hepher and Estelle Shirbon in Paris; Michael Connor in Miami; Writing by Terry Wade; Editing by Todd Benson and Kieran Murray)

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