  In a cycle of papers, starting with the present one, a fundamental
possibility of the polarization sounding of a pulsar magnetosphere using pulsar
self-radiation as a test signal will be considered. The main idea of such a
sounding is based on the fact that in some models of pulsar magnetosphere the
emission frequency depends on the height of its origin above the pulsar
surface. For this purpose it is needed to study the dependence of such a
parameter as the rotation measure on frequency and pulse phase. We expect that
it is possible to register the rotation measure dependence on the central
observing frequency and/or the pulse phase during the observations at widely
spaced frequencies in the same conditions. The reliable registration of this
dependence will result in resolving of the pulsar magnetosphere in depth. It is
preferably to carry out the polarization researches in the observational mode
of the individual pulses.
  In this part of the work the model of polarized pulsed radio emission and the
model of weakly anisotropic propagation medium are considered.
  In future articles we will show how to determine the polarization parameters
of pulsar radiation with the highest precision in presence of different types
of recorders on the receiving side. The specifics of polarization observations
at decameter wavelengths will be considered. The algorithms for solving the
inverse problem for different types of receivers and the variable conductivity
of the underlying surface will be developed.
