The proposal that President Obama has in his proposed budget does not specifically target Social Security. Rather his proposal would change how inflation is calculated which in turn adjusts how much Social Security's cost of living adjustment (COLA) increases each year and determining COLA's in other government programs as well as making changes to the tax code. Thus this proposed change would help alleviate the deficit problem by decreasing the amount of increase to government benefits and also increasing the amount of revenue gained in income taxes.
The proposal would change the calculation of inflation from using the standard consumer price index (CPI) to what is known as the Chained-CPI. Basically the Chained-CPI tries to more accurately adjust for consumer's actions when the price of a particular item increases. The standard CPI does this by using a lower-level substitution factor. For example, if the price of Granny Smith apples increases, people may change their purchasing habits by opting to buy Red Delicious apples instead. This lower-level substitution assumes that the consumer will make substitutions in their purchases among items in the same, low-level category (in the previous example, the low-level category being the variety of apples). However consumers won't necessarily just make substitutions in a particular category, but may opt to make a substitute with an item in a more general, higher-level category or a "mixed basket". So instead of making a substitution on the variety of apple, a consumer may decide instead to purchase pears (a higher-level "fruit" substitution) to the same increase in Granny Smith prices. The standard CPI does not take this higher-level substitution into account whereas the chained-CPI does, thereby making its calculation more in line with actual rates of inflation. By comparing the standard CPI vs the chained CPI in calculating inflation found that the standard CPI overestimated inflation by about 1%, so changing to this new method for inflation calculations would decrease the rate of growth for certain government programs.