The behaviour of a quantum particle moving in a system of N coupled chains parallel to each other and packed into a bundle is investigated in the presence of weak disorder. This system may be thought of as a model of an anisotropic thin wire. The dependence of the localization length r loc on N and t ⊥ is studied (t ⊥ is the interchain exchange integral characterizing the strength of the interchain tunneling). For t ⊥ < t c ≅ h/τ the localization length r loc increases proportionally to lt ⊥/(t τ −t ⊥) attaining a plateau value of the order of Nl (τ is the relaxation time and 1 the mean free path for elastic scattering). Such a behaviour may be called a transition from the Mott localization regime to the Thouless localization regime. It may be considered as a precursor of the insulator-metal transition (r loc → ∞) occuring for t ⊥ → t c in the quasi-1d system (N → ∞).