On the basis of quasiton theory an expression was obtained for the potential of interpartical attractive macroforces in a curved interface, being between liquid and gas, for a centrally symmetric case when the thickness DeltaL of the area under study is commensurable with the radius of curvature r(s) of a bubble or a drop. Expressions were also obtained for normal and tangential components of a stress tensor in the interface; using variational principles, it is shown that density profiles in the interface cannot be equilibrium, and there is a probability that the surface tension for the fine bubble or drop may be even negative.