  We consider an asymptotically free vectorial SU($N_c$) gauge theory with
$N_f$ fermions in the fundamental representation and analyze higher-loop
contributions to the evolution of the theory from the ultraviolet to the
infrared in the limit where $N_c \to \infty$ and $N_f \to \infty$ with
$r=N_f/N_c$ a fixed, finite constant. We focus on the case where the $n$-loop
beta function has an infrared zero, at $\xi=\xi_{IR,n\ell}$, where $\xi=\alpha
N_c$. We give results on $\xi_{IR,n\ell}$, the anomalous dimension of the
fermion bilinear evaluated at $\xi_{IR,n\ell}$, denoted $\gamma_{IR,n\ell}$,
and certain structural properties of the beta function, $\beta_\xi$. The
approach to this limit is investigated, and it is shown that the leading
correction terms are strongly suppressed, by the factor $1/N_c^2$. This
provides an understanding of a type of approximate universality in calculations
for moderate values of $N_c$ and $N_f$, namely that $\alpha_{IR,n\ell}N_c$,
$\gamma_{IR,n\ell}$, and structural properties of the beta function are similar
in theories with different values of $N_c$ and $N_f$ provided that they have
similar values of $N_f/N_c$. We give results up to four loops for
nonsupersymmetric theories and up to three loops for supersymmetric theories.
