By Carlos Quiroga

LA PAZ, July 25 (Reuters) - The state oil firms of Venezuela and Bolivia hope to start exploration in an Amazon national park next year as part of joint projects involving an investment of more than $1 billion, Bolivia's government said on Wednesday.

Venezuelan President Hugo Chavez is a close ideological ally of Bolivia's leftist leader, Evo Morales, and state-run PDVSA promised to invest in Bolivia after Morales nationalized his impoverished country's energy industry last year.

Bolivian Energy Minister Carlos Villegas said the investment would materialize in the first half of 2008 and would be channeled through Petroandina, a company formed by the powerful PDVSA and its smaller Bolivian counterpart, YPFB.

He said Petroandina would start exploring for oil next year in Bolivia's Madidi, a vast national park that stretches from the Andes to the Amazon basin and is said to be one of the most biodiverse areas on earth.

"I hope that in about eight months the work will already be getting started ... it inspires great hopes that we'll get good results in the north of La Paz province (Madidi)," Villegas said in comments distributed by his press office.

For PDVSA's investment to continue to advance as planned, Villegas said Congress must ratify the establishment of Petroandina and lift legal restrictions in order for exploration work to start in the Madidi reserve.

He noted that Morales had pledged to explore for oil in the poor, western region, where he has strong political support.

The country's natural gas-dominated energy industry is based in central and eastern Bolivia, where the rightist opposition to Morales is concentrated.

Villegas said that on a recent visit to Madidi with Morales they saw oil seeping from the ground in several places, though he said big investments would be needed in order to find out if the area had reserves with commercial importance.

Exploration rights in the area are also held by Spanish oil major Repsol <REP.MC>, Brazil's state-controlled Petrobras <PETR4.SA> and France's Total <TOTF.PA>.

As part of Morales' energy nationalization, all foreign companies operating in the country must present their own investment plans by the end of this month.

Bolivia, which has South America's largest natural has reserves after Venezuela, says those investments will allow it to double its gas output within five years in order to increase exports to Brazil and Argentina and meet its domestic needs.

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