convert this link to POST mode

Starx

Instead of creating a anchor tag. Create a hidden form

$linkword .= "n<A HREF="$self?letters=$alpha[$c]$letters&n=$n">$alpha[$c]</A>";

Here is a Sample

<form name="hiddenform" method="POST" action="page.php">
   <input type="hidden" name="letters" value="<? echo alpha[$c].$letters; ?>" />
   <input type="hidden" name="n" value="<? echo $n; ?>" />
   <a onclick="document.forms['hiddenform'].submit();">Test Link <? echo $alpha[$c]; ?></a>
</form>

Jsfiddle Demo