  The lower excitation spectrum of the nucleon and $\Delta$ is calculated in a
relativistic chiral quark model. Corrections to the baryon mass spectrum from
the second order self-energy and exchange diagrams induced by pion and gluon
fields are estimated in the field -theoretical framework. Convergent results
for the self-energy terms are obtained when including the intermediate quark
and antiquark states with a total momentum up to $j=25/2$. Relativistic
one-meson and color-magnetic one-gluon exchange forces are shown to generate
spin 0, 1, 2, etc. operators, which couple the lower and the upper components
of the two interacting valence quarks and yield reasonable matrix elements for
the lower excitation spectrum of the Nucleon and Delta. The only contribution
to the ground state nucleon and $\Delta$ comes from the spin 1 operators, which
correspond to the exchanged pion or gluon in the l=1 orbit, thus indicating,
that the both pion exchange and color-magnetic gluon exchange forces can
contribute to the spin of baryons. Is is shown also that the contribution of
the color-electric component of the gluon fields to the baryon spectrum is
enormously large (more than 500 MeV with a value $\alpha_s=0.65$) and one needs
to restrict to very small values of the strong coupling constant or to exclude
completely the gluon-loop corrections to the baryon spectrum. With this
restriction, the calculated spectrum reproduces the main properties of the
data, however needs further contribution from the two-pion exchange and
instanton induced exchange (for the nucleon sector) forces in consistence with
the realistic NN-interaction models.
