The former journalist will convey the socialist policies of new president Evo Morales, whose trademark striped sweater has earned him international publicity in recent weeks.
Contreras replaces former government spokesman Julio Pimentel. He reports to Morales, whose Movement Towards Socialism (MAS) party won a landslide victory last December, making him the nation's first indigenous president.
Contreras, formerly a news stringer for the BolPress agency, is currently forming his team and will soon name four people to handle 'key areas of government' according to an aide.
Bolivia, South America's poorest country, has its work cut out to emerge from its economic slump. As part of his socialist agenda, Morales has pledged to nationalise the country's bread-winning gas industry, pursue land reform and step up control of the economy. A former coca leaf grower and trade union leader, he intends to legalise coca leaf production.