CALCUTTA, INDIA, June 6.-East Pakistani refugees have carried the cholera epidemic inside the limits of this city of 12 million poverty-stricken inhabitants, leading to fears today of a massive outbreak.

About 12,000 refugees have slipped past government cordons around the city and set up a camp at the Salt Lake city housing project in northern Calcutta since Wednesday. Tens of thousands of other refugees are Crowding all approaches to Calcutta in their bid to reach the city.

At a refugee tent city of 40,000 on the city's outskirts, doctors said they were dealing with about 300 cases of cholera and gastro-enteritis. They said 14 persons had died there from what they called "choleric diarrhea in the past 48 hours.

To make matters worse, rain today turned the tent area into a lake of mud, adding the threat of typhus and typhoid to the cholera and gastro-enteritis already in the camp. Doctors also feared an outbreak of pneumonia.