Yes, the N-644 Form can be filed by someone who is not a U.S. citizen as long as they are eligible to apply on behalf of the deceased member of the U.S. armed forces. The person filing the N-644 Form must be either the surviving spouse, parent, child, sibling, or legal representative of the deceased member of the U.S. armed forces.
Although the person filing the N-644 Form does not need to be a U.S. citizen, they must be located in the United States and be able to provide the necessary information and documentation to support the application.