By Anthony Boadle

HAVANA, Dec 20 (Reuters) - Venezuelan President Hugo Chavez will assert his regional leadership at a summit in Cuba on Friday for Petrocaribe, his initiative to sell oil to Caribbean nations with soft financing.

With oil prices above $90 a barrel, Petrocaribe is offering terms that few can refuse, even the best allies of the United States: deferred payment of 40 percent of their oil bill for up to 25 years, at 1 percent interest.

"Hugo Chavez wants to use Petrocaribe to establish Venezuela as a regional power," said Dan Erikson, an expert on the Caribbean at the Inter-American Dialogue think tank.

He said Chavez is trying to win support from Caribbean countries "and show that he is basically a good guy trying to help small, poor countries in the region."

Chavez, a leftist with close ties to Cuban leader Fidel Castro and the U.S. government's main antagonist in Latin America, has already gained dividends, Erikson said.

A dozen heads of state will gather at the Cuban port city of Cienfuegos and attend the opening of a mothballed Soviet-era refinery that was refurbished by Venezuelan state oil company PDVSA, Cuban officials said.

They include President Daniel Ortega of Nicaragua, one of 16 Caribbean and Central American states now receiving about 190,000 barrels per day (bpd) of crude and products under the 2005 Petrocaribe deal, covering one-third of their imports.

Delegations from Guatemala and Honduras, countries that have traditionally been close to Washington, are keen to join up and will attend the Petrocaribe summit as observers.