Mikhail Prokhorov moved closer to taking control of the Nets on Tuesday night when he signed formal contracts to buy a controlling stake in the team and to invest in its Brooklyn arena project.

The deal with the current owner, the developer Bruce C. Ratner, is subject to approval by the N.B.A. Board of Governors. An N.B.A. spokesman, Michael Bass, said, ?We expect that the Board of Governors will vote on the application early in 2010.?

Prokhorov?s company, Onexim Sports and Entertainment Holdings, is paying $200 million for an 80 percent stake in the Nets and a 45 percent interest in the arena. He has also agreed to cover the team?s losses, up to $60 million, until the Nets move to the new arena, presumably by June 2012.