Admissions to California hospitals dropped in 1983 for the second straight year to 3.1 million from a peak of 3.2 million in 1981. The California Hospital Assn. said in an annual report on the latest admissions statistics that the decline in hospital use kept pace with the national trend. Analysts attribute much of the decline, which began in 1981, to the recession and a cutback in federal support for Medi-Cal programs for the poor. Those developments were followed by the Legislature's sharpest Medi-Cal cuts since the program began in 1966.