March 31, 1981

Sharply contrasting views of Joseph M. Margiotta were presented today by opposing counsel as his trial on charges of mail fraud and extortion began in Federal District Court here. The 53-year-old Nassau Republican leader was portrayed by Larry J. Silverman, an assistant United States attorney, in his opening statement as a politician who ''lined the pockets of his faithful supporters and lined his own pockets to the detriment of the people of Nassau County.'' Mr. Silverman depicted Mr. Margiotta as the mastermind, ''the one calling the shots,'' in a scheme to kick back insurance premium commissions from Hempstead Township and Nassau County to Republican politicians designated by Mr. Margiotta. The politicians did little or no work for the commissions.

AFTER years of debate, a growing number of psychiatrists and psychologists are concluding that even children can suffer from depression. Clinicians had long insisted that children under about 14 years of age lack the psychological capacity to experience depression, and some still remain skeptical. Dr. Jules Bemporad, a psychiatrist at Harvard Medical School, says, ''Real depression comes from attributing external events to oneself, but children can only look at life intuitively and do not search for reasons.'' Nevertheless, advances in the diagnosis and treatment of adult depression have generated research on the applicability of those advances to children. Scientists estimate that 5 to 20 percent of all adults are depressed. Their inability to pinpoint its incidence more accurately suggests that they are using different definitions of depression. They do agree, however, that depressed adults feel sad and worthless, and are hopeless about the future. Depressed adults also commonly experience loss of interest in pleasurable activities, a lack of energy and disturbances in their sleep.

Eight major international banks have agreed to establish a new $70 million credit to Jamaica's recently elected centrist Government, and to refinance another $103 million in loans owed by the country, it was disclosed yesterday. The agreement, which was reached last Friday, must be approved by 100 banks around the world that have loans outstanding to the Caribbean nation. The eight major banks, led by Citibank, represent a large portion of the $103 million in current Jamaican loans outstanding to foreign banks.

President Reagan was treated for a partly collapsed lung today, but the bullet that entered his left side and lodged in the tissue of his left lung did not do much further damage, according to doctors who operated on him. Surgeons removed a .22-caliber bullet from the President's lower left lung. Neither Mr. Reagan's heart nor such vital blood vessels as the aorta were affected, Dr. Dennis S. O'Leary, dean for clinical affairs at George Washington University, said at a briefing this evening. ''The bullet was never close to any vital structure,'' he said. He called Mr. Reagan's prognosis ''excellent.''

An article on Sunday in The Times's New Jersey Weekly incorrectly reported the circumstances under which Thomas Michalak accepted a position as music director of the Kansas City Philharmonic in Missouri. Mr. Michalak will continue as conductor of the New Jersey Symphony. His contract with the Missouri orchestra takes effect Wednesday and calls for him to be music adviser for the 1981-82 season and to serve an unspecified term as principal guest conductor.