An image compression encoding and decoding method and apparatus therefor is disclosed in which DC coefficients of a DCT block are scalar-quantized and AC coefficients are classified-vector-quantized (CVQ), and respective DCT blocks are classified by the least value of the square of the result that horizontal AC coefficients and vertical AC coefficients are subtracted from a representative value of a preset reference class. Using a multilevel compression method, lowest level codes are vector-partitioned by P-units with respect to each classified DCT block, and code books of representative vectors corresponding to the partitioned vectors are provided. Indices of corresponding representative vectors in respective code books and the classified codes are taken as encoding data corresponding to AC coefficients to keep a constant number of bits. Code books of S-units of representative vectors corresponding to errors are provided again, and corresponding indices and parity data in the respective code books are provided thereby performing a multi-level-classification-vector-quantization to be encoded. Decoding is performed in the reverse sequence of encoding. During a high speed search, only the lowest level codes having a constant number of bits are decoded regardless of the complexity of the picture.