  We perform comprehensive temporal and spectral analysis of the newly
discovered X-ray transient MAXI~J1803--298 using an AstroSat target of
opportunity observation on May 11, 2021 during its outburst. The source was
found to be in the hard intermediate state. We detect type C quasi-periodic
oscillations (QPOs) at the frequencies of $\sim5.4$ Hz and $\sim6.3$ Hz along
with a sub-harmonic at $\sim2.8$ Hz in the $3-15$ keV band. The frequency and
fractional rms amplitude of the QPO in the $15-30$ keV band are found to be
higher than those in the $3-15$ keV band. We find soft lags of $\sim3.8$ ms and
$\sim6.8$ ms for the respective QPOs at $\sim5.4$ Hz and $\sim6.3$ Hz, whereas
soft lag of $\sim4.7$ ms is found at the sub-harmonic frequency. The increase
in the soft lags at the QPO frequencies with energy is also observed in other
black hole transients and is attributed to the inclination dependence of the
lags. The rms-energy spectra indicate the power-law component to be more
variable than the disk and the reflection components. We find a broad iron line
with an equivalent width of $\sim0.17-0.19$ keV and a reflection hump above
$\sim12$ keV in the energy spectrum. Based on the X-ray spectroscopy and
considering the distance to the source as 8 kpc, the estimated mass
($\sim8.5-16$ M$_\odot$) and spin ($a\gtrsim0.7$) of the black hole suggest
that the source is likely to be a stellar mass Kerr black hole X-ray binary.
