First, let me say ugh. What are you using to parse this that it requires fixed length fields? Secondly, shouldn't you have closing tags starting with / instead of \?

Now how to fix your problem. It's pretty simple. If you output what is going to be evaluated, you'd realize that format will see @<<<<<<<\product. So it's misinterpreting what you really want. Replace the < that you want to show up with an @ and add "<" to the list of variables to fill it in. For more information on this, perldoc perlform.

$item="heat741a"; #for the sake of the example I  fixed the variables
$OrderQty = 55;
    open(LOG, ">order.xml") || die "Can't open the log file: $!\n";
    $format  = "format LOG = \n"
    . "\<\?xml version\=\"1\.0\"\?\>" . "\n"
    . "\<order\>" ."\n"
    . "\<product\>" .'@' . '<<<<<<' . '@' . "\\product\>" . "\n"
    . '$item,"<"'  . "\n"
    . "\<quantity\>" .'@' . '<' x (length($OrderQty)-1) . '@' . "\\qua
+ntity>" . "\n"
    . '$OrderQty,"<"'  . "\n"
    . "\<\\order\>" ."\n"
    . ".\n";

    eval $format;    
    write LOG;
    close LOG;
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Hope that helps.

antirice    
The first rule of Perl club is - use Perl
The ith rule of Perl club is - follow rule i - 1 for i > 1