* Citigroup will service portfolios through 1st half 2010
* Citigroup stock down 3.8 pct in afternoon trade

NEW YORK - Citigroup Inc said on Monday it sold three credit card portfolios representing $1.3 billion in managed assets, as part of a plan to unload weak businesses and troubled assets that caused huge losses.

The third largest U.S. bank by assets, which did not disclosed the terms of the deals, said it will continue to service the portfolios through the first half of 2010.

The cards portfolios were part of Citi Holdings, a division that includes assets the company is looking to shed or close over time.

In January, Citigroup -- hurt by mounting losses and toxic assets -- decided to separate into Citicorp, housing its key banking business, and Citi Holdings, which included its brokerage, consumer finance, and troubled assets.

The U.S. government injected $45 billion in Citigroup and is the bank's largest shareholder, with a roughly 34 percent stake.

Citigroup's shares were down 3.8 percent to $5.03 in Monday afternoon trading on the New York Stock Exchange. (Reporting by Juan Lagorio; Editing by Tim Dobbyn)