Conformal primaries of OSp(8/4,Bbb R) and BPS states in AdS4

We derive short UIR's of the OSp(8/4,) superalgebra of 3d N = 8 superconformal field theories by the requirement that the highest weight states are annihilated by a subset of the super-Poincare odd generators. We then find a superfield realization of these BPS saturated UIR's as ``composite operators'' of the two basic ultrashort ``supersingleton'' multiplets. These representations are the AdS4 analogue of BPS states preserving different fractions of supersymmetry and are therefore suitable to classify perturbative and non-perturbative excitations of M-theory compactifications.