  The in-plane and out-of-plane surface impedance and microwave conductivity
components of one and the same YBa_2Cu_3O_{7-x} (0.07\le x\le 0.47) single
crystal are determined in the wide ranges of temperature T and carrier
concentration p in CuO_2 planes. The following features of the superfluid
density n_s(T,p)\propto\lambda_{ab}^{-2}(T,p) are observed at T<Tc/2 and
0.078\le p\le 0.16: (i) n_s(0,p) depends linearly on p, (ii) the derivative
|dn_s(T,p)/dT|_{T\to 0} depends on p slightly in the optimally and moderately
doped regions (0.10<p\le 0.16); however, it rapidly increases with p further
lowering and (iii) the latter finding is accompanied by the linear
low-temperature dependence \Delta n_s(T)\propto(-T) changing to \Delta
n_s(T)\propto(-\sqrt{T}). For optimum oxygen content the temperature dependence
of the normalized imaginary part of the c-axis conductivity
\lambda_c^2(0)/\lambda_c^2(T) is found to be strikingly similar to that of
\lambda_{ab}^2(0)/\lambda_{ab}^2(T) and becomes more convex with p lowering.
\lambda_c^{-2}(0,p) values are roughly proportional to the normal state
conductivities \sigma_c(T_c,p) along the c-axis. All these properties can be
treated in the framework of d-density wave order of pseudogap.
