The number of cases of congenital syphilis in California increased more than threefold between 1983 and 1987, the state Department of Health Services announced. The department said that 72 syphilis infections, including 39 in Los Angeles County, were diagnosed in newborns last year, compared to 19 cases in 1983. So far this year, 56 additional cases have been reported. The number of congenital syphilis cases is low compared to the 9,000 cases of infectious syphilis diagnosed in teen-agers and adults last year. But infections in newborns usually have more serious complications, such as deformity, blindness or stillbirth. State officials said many of the cases were linked to prostitution, illicit drug use and inadequate prenatal care for the mother.