Oct 20 (Reuters) - Rodolphe Belmer will replace Elie Girard as chief executive of Atos by early next year, the French IT consulting firm said on Wednesday, in a sudden announcement that wrapped Girard's short stint as CEO.

Belmer, 52, is the current boss of French satellite firm Eutelsat, which he joined in 2015. A graduate of France's elite HEC business school, he previously led pay-TV station Canal+, owned by media group Vivendi.

Speculation about the future of Girard, 43, has mounted in recent months, following a string of setbacks that sent Atos' share price down by more than 40% this year.

The most painful stemmed from accounting errors spotted by auditors for two of Atos' units in North America. The disclosure in April spooked investors and triggered a 20% fall in the firm's shares in a single day.

The audit firm eventually cleared the accounts, but several analysts said the news had further dented investors' trust in Girard's management and strategy after a failed attempt to buy DXC Technology, a deal that valued the New-York listed group at more than $10 billion in what would have been the biggest-ever acquisition for deal-hungry Atos.

The group also cut its 2021 targets in July, blaming the ongoing COVID-19 pandemic.

The company's fall from investors' grace saw Atos exit France's blue-chip CAC 40 index last month and speculation about a takeover or the arrival of activist investors.

Girard, who will leave the company on Friday, succeeded Thierry Breton, today's European industry chief, in 2019, after acting as a close aide to the former French finance minister as CFO.

A former top executive at telecoms group Orange, Girard inherited a company that had rapidly expanded through a buyout spree, which included cloud and cybersecurity firm Bull.

Atos, which plans to gradually dispose of non-core assets and seek partners for classic infrastructure activities, said Belmer's term of office would begin on Jan. 20, 2022, at the latest.

Effective Monday, Oct. 25, Pierre Barnabe and Adrian Gregory would be appointed acting co-chief executive officers until Belmer starts, the company said. (Reporting by Mathieu Rosemain, Gwenaelle Barzic, Bartosz Dabrowski and Juliette Portala in Gdansk; editing by Christian Lowe, Kirsten Donovan)