BRASILIA, Dec 6 (Reuters) - A reshuffle in Brazil's Economy Ministry will put a key aide to Minister Paulo Guedes in charge of promoting private-sector investments, a person with knowledge of the matter said on Monday, in a push to combat growing financial market pessimism about the country's growth prospects.

Daniella Marques, who worked with Guedes at investment firm Bozano Investimentos before they both joined the government, has long been considered his closest aide and serves now as special advisor on strategic affairs.

She will be soon named secretary of productivity and competitiveness at the ministry, replacing Carlos da Costa, who will be appointed trade attache to the United States, said the source, requesting anonymity to discuss confidential plans.

Guedes has said contracted private investments worth more than 700 billion reais (123.5 billions) over the next 10 years will help the economy from 2022 onward, pushing back against falling market forecasts for economic growth next year.

That pessimism was reinforced by a 0.1% contraction of gross domestic product last quarter, marking a recession https://www.reuters.com/markets/us/brazil-economy-recession-after-q3-contraction-2021-12-02 in Latin America's largest economy.

Guedes has also tapped fiscal auditor Julio Cesar Vieira Gomes to replace Jose Tostes Neto as head of federal revenue at the ministry, the source said. Tostes Neto is set to become Brazil's representative to the Organization of Economic Cooperation and Development (OECD).

The government has not yet settled on who will lead the ministry's political coordination with Congress. President Jair Bolsonaro vetoed the first choice of Guedes, former lawmaker Alexandre Baldy.

Baldy, who was previously the cities minister under former President Michel Temer, has worked with Sao Paulo Governor Joao Doria, a potential rival of Bolsonaro in next year's election.

The political coordination role has been vacant since Esteves Colnago was appointed as special secretary of the Treasury after several key ministry officials quit in protest of looser spending rules ahead of the 2022 election.

($1 = 5.67 reais) (Reporting by Marcela Ayres Editing by Brad Haynes and Paul Simao)