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We perform comprehensive temporal and spectral analysis of the newlydiscovered X-ray transient MAXI~J1803--298 using an AstroSat target ofopportunity observation on May 11, 2021 during its outburst. The source wasfound to be in the hard intermediate state. We detect type C quasi-periodicoscillations (QPOs) at the frequencies of $\sim5.4$ Hz and $\sim6.3$ Hz alongwith a sub-harmonic at $\sim2.8$ Hz in the $3-15$ keV band. The frequency andfractional rms amplitude of the QPO in the $15-30$ keV band are found to behigher 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, whereassoft lag of $\sim4.7$ ms is found at the sub-harmonic frequency. The increasein the soft lags at the QPO frequencies with energy is also observed in otherblack hole transients and is attributed to the inclination dependence of thelags. The rms-energy spectra indicate the power-law component to be morevariable than the disk and the reflection components. We find a broad iron linewith 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 andconsidering 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 suggestthat the source is likely to be a stellar mass Kerr black hole X-ray binary.

AstroSat view of the newly discovered X-ray transient MAXI~J1803--298 in the Hard-intermediate state