We report on the probable X-ray detection, using the Chandra X-Ray Observat
ory, of the Type II-plateau (II-P) supernova SN 1999gi in the spiral galaxy
NGC 3184. A faint source is located within 0."4 of the supernova's optical
position. The inferred luminosity is similar to1 x 10(37) ergs s(-1) in th
e 0.5-10 keV band for an adopted 1 keV thermal bremsstrahlung spectrum. The
luminosity from SN 1999gi is very similar to that inferred from the Chandr
a detection of the Type II-P SN 1999em in NGC 1637 for which we extracted d
ata from the Chandra archive. We suggest that Type II-P supernovae show X-r
ays initially at outburst, subsequently fade, and are not significant X-ray
emitters prior to the remnant stage.