Assigning ASCII values to the plaintext alphabets during transmission of documents is very common, and as we know that the ASCII value of `a' is less than that of `z'. But, what would happen if the document contains more `z' as compared to `a'. In that case, achieving security through encryption - decryption and compression is very difficult. This paper proposes a technique of assigning codes to plain text alphabets, based on the frequency of occurrences of those alphabets by using ant colony optimization with roulette wheel selection algorithm, so that security in code generation could be achieved. Obtained codes are then applied over a particular encryption algorithm such that the cipher text generated should contain those alphabets only whose code values are near about similar to that of plain text alphabets, in order to achieve compression simultaneously. Getting all this within specified time constraint makes this paper more impressive.