By Sudip Kar-Gupta

PARIS (Reuters) - France's biggest listed bank, BNP Paribas (BNPP.PA: Quote, Profile, Research), beat most expectations despite a 21 percent fall in first-quarter net profit on Wednesday as growth at its retail bank cushioned a plunge at its investment bank.

First quarter net profit fell to 1.981 billion euros ($3.1 billion) as BNP Paribas' investment banking division made a 514 million euro writedown due to the impact of the credit crunch.

The result beat an average net profit forecast of 1.675 billion euros from a Reuters poll of 20 analysts.

Gross operating profit fell 23 percent to 2.79 billion euros, below an average forecast of 2.89 billion.

Shares were up 3.2 percent at 69.66 euros in early afternoon trade as analysts welcomed the results. The stock was among the top gainers on France's benchmark CAC-40 index .FCHI which was up 0.4 percent.

"The figures were better than expected and especially solid in their retail bank arm," said Stratege Finance fund manager Valerie Cazaban, who holds BNP Paribas shares.

GSD Gestion fund manager Christophe Gautier, who also holds the stock, said BNP Paribas had fared better than many of its rivals.

"They haven't made as many writedowns as the Anglo-Saxon banks," he said. In April, Citigroup (C.N: Quote, Profile, Research) posted a $5.1 billion quarterly loss that reflected more than $16 billion of writedowns and credit-related costs.