AIX

Rexec executes commands one at a time on a remote host. The rexec command provides an automatic login feature by checking for a $HOME/.netrc file. User and password are stored
in $HOME/.netrc.

I would like to log on to another host and execute a script/command but not using $HOME/.netrc file, rather something like
Command user password host remote-command.

Which command/approach can I use instead of rexec (AIX Unix)?

To automate this Expect might help. It is available from the IBM AIX Linux Toolbox.

Or set up ssh authentification by exchanging public keys and do it by ssh/scp.

zaxxon, shockneck -> are there a basic command i can use out of the box? so I can avoid configuration of extra functionality.

ssh should be available. Not sure on which version of AIX (5.2?) it became standard. You will have to generate a private and public key without entering a password when being asked at creation (ssh-keygen) for the user. They will be place under ~/.ssh. To have passwordless authentication you will have to add the pub-key of the "client" to the authorized_keys file of the remote host to grant access.
There should be some posts here in the forum or on the web how to set it up step by step.