Spectroscopic and photometric observations of supernova 1987A. VII. Days 793 to 1770.

We present spectroscopic and UBV(RI)_C_JHKLM photometric observations of SN 1987A in the Large Magellanic Cloud made between days 793 and 1770 after the Kamiokande-II neutrino event, as well as some CCD UBV(RI)_C_ photometry from day 640 to day 792, which overlaps the interval covered in the preceding paper of this series. During the period from about day 670 to day 1260, the U to M- bolometric magnitude (hereafter M_UM_) of the supernova and its adjoining circumstellar ring (hereafter 'the enclosed supernova') dimmed at an increasingly slower rate than during the preceding interval from day 500 to day 670. The rate of dimming steadily increased again between days 1270 and 1770. From day 1000 onwards, the light of the circumstellar ring made an increasingly significant contribution to the light of the enclosed supernova, and by day 1250 had become so dominant that it is probable that useful Earth based photometry of the bare supernova itself was not feasible thereafter.