  We study the critical behavior of frustrated spin models with noncollinear
order in two dimensions, including antiferromagnets on a triangular lattice and
fully frustrated antiferromagnets. For this purpose we consider the
corresponding $O(N) \times O(2)$ Landau-Ginzburg-Wilson (LGW) Hamiltonian and
compute the field-theoretic expansion to four loops and determine its
large-order behavior. We show the existence of a stable fixed point for the
physically relevant cases of two- and three-component spin models. We also give
a prediction for the critical exponent $\eta$ which is $\eta =0.24(6)$ and
$\eta =0.29(5)$ for N=3 and 2 respectively.
