Most interlaced stuff is lower field first nowadays. Just to be sure, do this:
1. interpret the footage and separate fields.
2. Alt-double-click on the footage.
3. In the window that appears, step through the footage using the PageDn key. If the footage moves in one direction, you picked the right field order, and you can close the window and go back to work. But if the footage goes back and forth as you step through it by hitting the pageDn key, you picked the wrong field order, and you need to re-interpret the footage, picking the other field order.
Just for fun, pick the “wrong” order, so you can see the footage go back and forth.
By the way, other apps call this “field dominance”, but it’s really “field order”.