S&P; downgraded Mission Insurance debentures.

Standard & Poor’s cited the Los Angeles-based property-casualty insurer’s recently reported $198.1-million 1984 loss and a drop in equity capital to $8.5 million from $215.7 million during the year in lowering its rating from BB-Plus to B-Minus on the sinking-fund debentures, which total $71 million--a 9% debenture issue due 2002 and an 11.875% issue due 1993. “The $198.1-million, full-year loss suggests that the company’s efforts to restore capital to a viable level will be difficult and perhaps prolonged,” S&P; said.