  We study a generalized superconformal model that gives rise to a subcritical
regime of $D$-term hybrid inflation. Exhibiting the model both in a Jordan
frame and in the Einstein frame, the effective potential of the subcritical
regime is derived in the Einstein frame. It turns out the inflaton-waterfall
field dynamics leads to various types of inflaton potential. Consequently the
tensor-to-scalar ratio is found to range from $10^{-4}$ ($10^{-3}$) to $0.1$
for getting 60 (50) $e$-folds before the end of inflation.
