If you worked under the social security system of a foreign country, the periods of work may be taken into account toward meeting U.S. insured status requirements for the U.S. Social Security Act’s title II retirement, survivors, and disability insurance programs if:
A social security agreement between the U.S. and the foreign country (Totalization agreement) (see §107) provides for counting the foreign periods of coverage;
You have at least six credits earned under the U.S. program; and
You would not be insured for benefits without taking the foreign periods into account.
If you qualify for benefits using combined coverage, the amount payable is based on a U.S. primary insurance amount (see Chapter 7). This is pro rated to reflect the fact that although foreign coverage helped you acquire insured status, the benefit payable is based on your U.S. coverage only.
http://www.ssa.gov/international/agreement_descriptions.html
Last Revised: Aug. 8, 2011