''It's going to be a challenging quarter from the mark- to-market of the investment portfolios, to the charge-offs of loans primarily in the consumer area, mortgages, home-equity loans, credit cards and auto finance.'' Pandit's Strategy Citigroup on April 18 will probably report a loss of $US4.75 billion, the average of 6 analysts' estimates compiled by Bloomberg. Chief executive Vikram Pandit is selling loans and securities to raise capital and has slashed more than 6000 jobs while conducting what he calls a ''front-to-back review'' of businesses that stretch across more than 100 countries. Analysts have lowered their estimates over the past three months. Citigroup was expected to earn about 90 cents a share as recently as January. Now they expect the company to post a loss of 93 cents a share. JPMorgan, working to integrate its acquisition of investment bank Bear Stearns, is expected to report earnings on April 16 of 68 cents a share, based on the average estimate of 15 analysts surveyed by Bloomberg.