There used to be an official editor, Heavy Metal Pro / Aero / Vee, however it has not been maintained for quite some time, and does not have support for all Total Warfare weapons and rules (They can be added with custom files, etc, but it is not native support).
Catalyst have stated in the past that they are open to someone approaching them about making a new official software, but until that time, other editors are fine for most* use.
* Official games run by Agents try hard to use official released record sheets and official designs, rather than custom units.