NEW YORK - Citigroup Inc. named Vikram Pandit, the head of its investment-banking business, as chief executive yesterday, after searching five weeks for someone to restore the bank's profitability and reputation.

The banking company named Sir Win Bischoff, who has been Citi's acting CEO, as its chairman. He replaces Robert E. Rubin, who had stepped into the role when former CEO and chairman Charles Prince was ousted last month.

Pandit, 50, ran a hedge fund bought by Citi earlier this year, and is seen as a careful, decisive investment banker - qualities Citi needs following the revelation that Citi's writedowns of soured mortgages could amount to as much as $17.5 billion by the end of the year.

Bischoff, 66, has led Citi's European businesses.

Citi's shares fell $1.54, or 4.4 percent, to $33.23 yesterday, when most shares fell. *