Nonlinear Realizations of Superconformal and W Algebras Embeddings of Strings

We propose a simple method for constructing representations od (super) conformal and nonlinear W-type algebras in terms of their subalgebras and coresponding Nambu-Goldstone fields. We apply it to N=2 and N=1 superconformal algebras and describe in this subalgebras define world-sheet symmetries. Besides reproducing the known exmples, we present some new ones, in particular an embedding of the bosonic string with additionsl U(1) affine symmetry into N=2 superstring. We also apply our method to the nonlinear W(2)3 algebra and demonstrate that the linearization procedure worked out for it some time ago gets a natural interpretation as kind of string embedding. All these embeddingd include the critial ones as particular cases.