in AIX 4.3.3, the default ftp client does not support the chmod command as show in the following output:

/plib/dwl0/temp $ ftp 127.0.0.1
Connected to 127.0.0.1.
220 rs6k660a FTP server (Version 4.1 Wed Feb 27 11:03:17 CST 2002) ready.
331 Password required for db2adm00.
230 User db2adm00 logged in.
ftp> help
Commands may be abbreviated. Commands are:

! image recv
$ lcd reget
account local reinitialize
append ls remotehelp
ascii macdef rename
bell mdelete reset
binary mdir restart
block mget rhelp
bye mkdir rmdir
carriage-control mls rstatus
case mode runique
cd modtime safe
cdup mount send
clear mput sendport
close nmap site
copylocal nlist size
cr non-print status
delete ntrans stream
debug open struct
dir passive sunique
disconnect private system
ebcdic prompt telnet
exp_cmd protect tenex
file proxy trace
form put type
get pwd user
glob quit verbose
hash quote ?
help record
ftp>

does anyone has an idea how to chmod of the remote file from ftp client?
or is there any way to execute a remote command to act like a chmod ?

If it is a unix box your ftp'ing could you not use rsh to carry out chmod, instead of using FTP

Try:
ftp> init chmod 777 filename
(works on AIX even though it's not in the helps)...