UPDATE 2-Union to launch Petrobras strike ahead of talks

(Updates with quotes from Petrobras president)

RIO DE JANEIRO, July 11 (Reuters) - Brazilian oil workers will begin a five-day strike at the country's main fields in the Campos basin on Monday, regardless of whether state-oil company Petrobras presents a proposal before then, a union official said on Friday.

Campos accounts for more than 80 percent of Brazil's crude output of 1.8 million barrels per day.

"The decision has been taken to only negotiate with the strike on," said Jose Genivaldo Silva, director of the United Oil Workers' Federation, an umbrella union.

An official at the local Campos basin union confirmed the information, saying the strike will start on Monday at all the 42 Campos offshore platforms.

"Petrobras can make another offer before then, but we'll hold the strike. Platforms will only operate to maintain safety," said a union official who gave only his first name, Genilson.

The Campos union demands that Petrobras count the day workers leave the platform for the shore as a working day.

Petrobras Chief Executive Jose Sergio Gabrielli said the company was preparing a contingency plan and that it remains open to negotiations.

"We are negotiating, we are open, and we're of the nature to avoid the strike so that it doesn't affect production," Gabrielli told journalists in Sao Paulo on Friday. "Production will continue. We will, if needed, implement a contingency plan to maintain minimum staffing to continue producing."

Worries about the potential strike helped push up world oil prices on Thursday, propping it to new record on Friday.

"Petrobras is telling us every day that it is open to negotiations, they receive us nicely and all but then they say they've already made their final offer," Silva said.

Separately, the umbrella union will hold a meeting Tuesday to discuss the possibility of a five-day nationwide strike at all Petrobras facilities, including refineries and terminals, to demand a bigger share of company profits for workers.

A five-day nationwide strike of Petrobras workers in 2001 seriously reduced output and forced Brazil to import additional oil. Unions and the company have resolved their differences over the past few years without stoppages hurting production. ($1=1.61 reais) (Reporting by Andrei Khalip and Reese Ewing; Editing by Marguerita Choy)