This situation actually occurs frequently. One can file the N-400 application for naturalization (i.e., citizenship) while the I-751 is still pending. However, the N-400 cannot be approved until the I-751 has been approved. Occasionally, USCIS officers will have both files, and conduct interviews for both simultaneously. However, more frequently, the N-400 interview will be conducted, and the case will be placed “on hold” until the I-751 is finally approved. (15.Jun.2020)
