  Repeated imaging observations have been made of NGC 3982 with the Hubble
Space Telescope between March and May 2000, over an interval of 53 days. Images
were obtained on 12 epochs in the F555W band and on five epochs in the F814W
band. The galaxy hosted the type Ia supernova SN1998aq.
  A total of 26 Cepheid candidates were identified, with periods ranging from
10 to 45 days, using photometry with the DoPHOT program. The de-reddened
distance to NGC 3982 is estimated from these data using various criteria to
maximize signal to noise and reliability: the values lie between 31.71 and
31.82, with uncertainties in the mean of typically +/- 0.14 mag for each case.
A parallel analysis using photometry with HSTphot discovered 13 variables,
yielding a distance modulus of 31.85 +/- 0.16. The final adopted modulus is
(M-m)_0 = 31.72 +/- 0.14 (22 +/- 1.5 Mpc).
  Photometry of 1998aq that is available in the literature is used in
combination with the derived distance to NGC 3982 to obtain the peak absolute
magnitude of this supernova. The lower limit (no extinction within the host
galaxy) for M_V is -19.47 +/- 0.15 mag. Corrections for decline rate and
intrinsic color to carry these to the reduced system of Parodi et al. (2000)
have been performed. The derived luminosities at hand are fully consistent with
the mean of the 8 normal SNe Ia previously calibrated with Cepheids. Together
they yield H_0 ~ 60 +/- 2 (internal) km s-1 Mpc-1 based on an assumed LMC
distance modulus of 18.50. We point out that correcting some of the systematic
errors and including uncertainty estimates due to them leads to H_0 = 58.7 +/-
6.3 (internal) km s-1 Mpc-1.
