We have obtained optical ( BVR , [ O iii ] \lambda 5007Å and H \alpha ) , near infrared ( JHK ) imaging and long-slit optical spectroscopy for the Blue Compact Dwarf galaxy Mrk~86 ( NGC~2537 ) .
In this paper , the first of two , we present optical-near-infrared colors and emission-line fluxes for the currently star-forming regions , intemediate aged starburst and underlying stellar population .
We also describe the evolutionary synthesis models used in Paper II .

The R and H \alpha luminosity distributions of the galaxy star-forming regions show maxima at M _ { R } = - 9.5 ^ { \mathrm { m } } and L _ { \mathrm { H } \alpha } =10 ^ { 37.3 } erg s ^ { -1 } .
The underlying stellar population shows an exponential surface brigthness profile with central value , \mu _ { \mathrm { E, 0 } } =21.5 mag arcsec ^ { -2 } , and scale , \alpha =0.88 kpc , both measured in the R -band image .
In the galaxy outer regions , dominated by this component , no significant color gradients are observed .

Finally , a complete set of evolutionary synthesis models have been developed , covering a wide range in metallicity , 1/50 Z _ { \sun } < Z < 2 Z _ { \sun } , and burst strength , 1-10 ^ { -4 } .
These models include nebular continuum and recombination and forbidden-line emission .