This paper presents a control architecture for safe and smooth navigation of a group of Unmanned Ground Vehicles (UGV) while keeping a specific formation. The formation control is based on Leader-follower and Behavioral approaches. The proposed control architecture is designed to allow the use of a single control law for different multi-vehicle contexts (navigation in formation, transition between different formation shapes, obstacle avoidance, etc.). The obstacle avoidance strategy is based on the limit-cycle approach while taking into account the dimension of the formation. A new Strategy for Formation Reconfiguration (SFR) of the group of UGVs based on suitable smooth switching of the set-points (according, for instance , to the encountered obstacles or the new task to achieve) is proposed. The inter-vehicles collisions are avoided during the SFR using a penalty function acting on the vehicle velocities. Different simulations on cluttered environments show the performance and the efficiency of the proposal, to obtain fully reactive and distributed control strategy for the navigation in formation of a group of UGVs.