  Nearly 400 Tycho-2 stars have been observed in a 720 square degree field in
the direction of the North Galactic Pole with the high resolution echelle
spectrograph ELODIE. Absolute magnitudes, effective temperatures, gravities and
metallicities have been estimated, as well as distances and 3D velocities. Most
of these stars are clump giants and span typical distances from 200pc to 800pc
to the galactic mid-plane. This new sample, free of any kinematical and
metallicity bias, is used to investigate the vertical distribution of disk
stars. The old thin disk and thick disk populations are deconvolved from the
velocity-metallicity distribution of the sample and their parameters are
determined. The thick disk is found to have a moderate rotational lag of -51+-5
km/s with respect to the Sun with velocity ellipsoid (sigma_U, sigma_V,
sigma_W)=(63+-6, 39+-4, 39+-4) km/s, mean metallicity of [Fe/H]=-0.48+-0.05 and
a high local normalization of 15+-7%. Combining this NGP sample with a local
sample of giant stars from the Hipparcos catalogue, the orientation of the
velocity ellipsoid is investigated as a function of distance to the plane and
metallicity. We find no vertex deviation for old stars, consistent with an
axisymmetric Galaxy. Paper II is devoted to the dynamical analysis of the
sample, puting new constraints on the vertical force perpendicular to the
galactic plane and on the total mass density in the galactic plane.
