BODY: Governor Mitt Romney yesterday signed into law a permanent ban on deadly assault weapons, such as the AK-47 and Uzi, made or sold in Massachusetts. The current state ban, passed in 1998, is tied to a federal law that is set to expire Sept. 13 unless Congress reauthorizes it. President Bush has signaled that he would sign a bill extending the ban, but state officials had worried that Congress might not approve a new bill before the expiration. Activists say Massachusetts is the first state to extend the ban