A banking analyst at Oppenheimer & Co said that when big banks proclaim that they are performing well, they better be right.

In a report previewing first-quarter results for some of the largest U.S. banks, analyst Chris Kotowski noted how Bank of America Corp , Citigroup Inc , JPMorgan Chase & Co and Britain's Barclays Plc have all made upbeat comments about their early 2009 performance.

While many analysts expect the pace of writedowns for toxic assets to slow throughout the industry, the deterioration in credit quality shows no signs of ending, as many of the world's major economies suffer through a deep recession.

With share prices of many banks far below where they were before the global credit crisis took hold in 2007, banks need to be careful not to inflame suffering shareholders.

Bank of America, Citigroup, JPMorgan and Barclays publicly proclaimed optimism about profitability in the first quarter based on their favorable experience in January and February, Kotowski wrote. All of which means that barring an act of God, they had better report some number that is in the black or potentially risk being involved in some of the most intense securities litigation on record.

According to Reuters Estimates, analysts on average believe Bank of America and JPMorgan made money in the first quarter, excluding items, but expect Citigroup to post a loss. Quarterly forecasts for Barclays were not available.

(Reporting by Jonathan Stempel; Editing by Tim Dobbyn)