1. A method for interactive voice recognition of a word by a voice recognition system, which comprises the steps of: performing a word recognition mode by the steps of: converting a spoken word into an electrical word voice signal; analyzing the electrical word voice signal for recognizing the spoken word from a vocabulary of predetermined words; performing the following steps if a definite assignment of the electrical word voice signal to a word from the vocabulary of predetermined words cannot be made: compiling a preselection of words from the vocabulary of predetermined words which have a sufficient probability of being the spoken word; determining for each word forming the preselection of words, at least one decisive letter which makes the word distinguishable from other words in the preselection of words; inquiring which of the decisive letters for the words of the preselection of words is appropriate during a spelling recognition mode; converting a spelling voice input into an assigned electrical spelling voice signal; and analyzing the assigned electrical spelling voice signal for recognizing the decisive letter.