Export of RSA falls under the same U.S. laws as all other cryptographic products.
RSA used for authentication is more easily exported than when it is used for privacy. In the former case, export is allowed regardless of key (modulus) size, although the exporter must demonstrate that the product cannot be easily converted to use for encryption. In the case of RSA used for privacy (encryption), the U.S. government generally does not allow export if the key size exceeds 512 bits.
Export policy is currently a subject of debate, and the export status of RSA may well change in the next year or two. For example, a Commerce Jurisdiction (basically a general export license per Department of Commerce rather than Department of State approval) has been obtained by Cybercash for 768-bit RSA for financial transactions.
Regardless of U.S. export policy, RSA is available abroad in non-U.S. products.