NSF allows one to submit grant proposals through http://grants.gov (new system) or http://www.fastlane.nsf.gov (good old system). One should ask his local Office of Research which one should be used. SSN is needed to register a new account in Fastlane if one wants to do it by himself. It is not always available for a foreigner who just arrives in US. A easy way to do it is to ask the Office of Research to do it for you. The requirement on SSN is bypassed this way. You will be given enough information to login afterward.