Thanks for taking your time to answer, Iñaki, and I'm sorry for my delayed answer.
What I want is to create a user on Moodle, and set Moodle to automatically send the values "Username" and "Password" of this new user to LDAP, also creating a new entry there automatically (if it's possible before they log in) . So I'll have my user on Moodle database and the fields name and password on LDAP database.
My Moodle users are configured to have CAS authentication (CAS plugin for Moodle activated, and configured with my CAS and LDAP properties), so if I want to log in as a Moodle user, it sends me to jasig CAS log-in interface, there I put my Moodle-user credentials (username and pass) , and CAS compares it with the entries of my LDAP. If user and password matches with any entry of my LDAP, the authentication success and I can navigate on Moodle. That's why I want it.
I'm not experienced with Moodle, and I've been checking some php's like /cas/cli/sync_users.php . But it does exactly the opposite to what I want, creating users in Moodle with the new values of my LDAP.
So, what I'm trying to do now is my own php integrated on externallib.php to connect LDAP and write users with the name and password values of the Moodle user creation.
I hope I could explain it better now, and thank you again!