Following our recent development of the paradigm for extending the classic concepts of circuit elements to the infrared and optical frequencies [N. Engheta, A. Salandrino, A. Alù, Phys. Rev. Lett. 95, 095504 (2005)], in this paper we investigate the possibility of connecting nanoparticles in series and in parallel configurations, acting as nanocircuit elements, In particular, we analyze a pair of conjoined half-cylinders, whose relatively simple geometry may be studied and analyzed analytically. In this first part of the work, we derive a closed-form quasi-static analytical solution of the boundary-value problem associated with this geometry, which will be applied in Part II for a nanocircuit and physical interpretation of these results.OCIS codes: 999.999 (Nanocircuits), 350.4600, 240.6680, 290.5850.