Can my Tribe write a letter of support for a state-led partnership application, even if my organization does not directly participate in the project as an EN partner?

Yes- Tribal and other entities are welcome to provide letters of support for applications.  A letter of support on its own would not inherently count an organization as a partner in the application. To avoid any confusion on EPA’s part, however, please be sure that it is very clear in the submitted project narrative who the partnering organizations are (so there is no confusion on this additional support letter).