  We present the theory of two-dimensional, clean quantum antiferromagnets with
a small, positive, zero temperature ($T$) stiffness $\rho_s$, but with the
ratio $k_B T / \rho_s $ arbitrary. Universal scaling forms for the uniform
susceptibility ($\chi_u$), correlation length($\xi$), and NMR relaxation rate
($1/T_1$) are proposed and computed in a $1/N$ expansion and by Mont\'{e}-Carlo
simulations. For large $k_B T/\rho_s$, $\chi_u (T)/T$ and $T\xi(T)$ asymptote
to universal values, while $1/T_{1}(T)$ is nearly $T$-independent. We find good
quantitative agreement with experiments and some numerical studies on
$La_{2-\delta} Sr_{\delta} Cu O_4$.
