JAKARTA, Aug 28 (Reuters) - A U.S. salvage company has retrieved the flight data and cockpit voice recorders from an Indonesian plane that crashed into the ocean in January with 102 people on board, officials said on Tuesday.

The Boeing 737-400, operated by budget carrier Adam Air, went down on New Year's day in the sea off south Sulawesi in one of the country's worst air disasters.

An underwater robot scouring the sea off Majene on Sulawesi retrieved the flight data recorder on Monday and cockpit voice recorder on Tuesday, said Tatang Kurniadi, chief of the Indonesian Transport Safety Commission.

The two devices were found at a depth of around 2,000 metres (6,500 ft) and were 1,400 metres apart, he said.

The search effort was conducted by the U.S. seabed salvage company, Phoenix International, in cooperation with the U.S. National Transport Safety Board and the Indonesian commission.

"The blackbox will be sent to Washington for analysis," Kurniadi told a news conference in Jakarta. The analysis to try to determine the cause of the accident could take months, he added.

The black box refers to the flight data recorder and cockpit voice recorder.

Efforts to recover the black box were delayed due to disagreements between the government and Adam Air over who should bear the cost.

The 17-year-old plane was heading from Surabaya in East Java to Manado in northern Sulawesi when it vanished in bad weather. The plane made no distress call, although the pilot had reported concerns over crosswinds.

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