ftp_chmod(ftp_connection,mode,file)

<?php
$conn = ftp_connect("ftp.testftp.com") or die("Could not connect");
ftp_login($conn,"user","pass");

// Read and write for owner, nothing for everybody else
ftp_chmod($conn,"0600","test.txt");

// Read and write for owner, read for everybody else
ftp_chmod($conn,"0644","test.txt");

// Everything for owner, read and execute for everybody else
ftp_chmod($conn,"0755","test.txt");

// Everything for owner, read for owner's group
ftp_chmod($conn,"0740","test.txt");

ftp_close($conn);
?>