The solution of a linearized gas-kinetic equation and a model collision integral are used to calculate the force acting on an unevenly-heated particle in an isothermal gas flow. A closed system of integral-moment equations is constructed to describe the problem with arbitrary values of the Knudsen number and an arbitrary ratio of the thermal conductivities of the particle and gas. Allowance is made for the possibility of arbitrary accommodation of momentum and energy in the interaction of a gas molecule with the particle surface. The system of equations is solved by the Bubnov-Galerkin method. An analysis is made of the effect of the governing parameters of the problem on the isothermal drag, radiometric force, and thermal polarization of the particle. The results obtained are compared with the well-known theoretical and experimental data.