CALCUTTA, India, May 31 —Indian health authorities made an urgent appeal today for international assistance as Government doctors announced that an uncontrollable epidemic of cholera had broken out among the millions of Bengali refugees who have crossed into India from East Pakistan.

An unknown number of people have already died of cholera and thousands are reported collapsing with the disease every day. Doctors suspect that the thousands of Bengalis crossing the frontier every hour are al ready affected by the disease.