You could use operator ||, or even use the or keyword:
if ($page == "topfriends" || $page == "word2" || $page == "word3") {
include "config/country_Sajax.php";
}
Alternatively, a switch/case structure might be appropriate. If the list of words to compare is long, perhaps [man]in_array/man with an array of those words would be more suitable.