But even as J. P. Morgan executives stressed that they expected smaller losses this year in areas like corporate lending and venture capital, they were wary of predicting a rebound in the core investment banking business. Investment banking has reported disappointing results since J. P. Morgan merged with Chase Manhattan in December 2000. ''We don't have evidence yet for a rosier near-term outlook,'' Dina Dublon, J. P. Morgan's chief financial officer, said in a conference call with analysts yesterday.