Although it's estimated that there are around 20,000 shipwrecks off United States' coastlines, the problem of pollution from shipwrecked vessels is much more manageable than that number suggests.
Of those 20,000, many did not run on oil, and coal is much less of a pollution risk in submerged vessels. Of those that did run on oil, many have since stopped leaking, or are located away from sensitive US land. Only 87 of the shipwrecked ships still have the potential to leak tens of millions of gallons of oil, and only 6 of those have the potential (due to location and other factors) to severely damage local economies and coastlines.
Most of the 87 ships were lost during World War II - sunk by German U-boats within Just because the ship is known lost in a certain area, however, doesn't mean the location of the shipwreck is known. Not all of the 87 potential leakers have been precisely located, and at least one (the Edmund Fitzgerald) isn't even located in US waters. So far 17 shipwrecks have been precisely located and need to be investigated to see if it is possible to drain the oil from the ship before it leaks into the open ocean.
Although there is potential for some damaging local pollution from many of these wrecks, the total potential spill from all 87 wrecks is less than half the 200 million gallons that spilled from the BP well in 2010.
The complete report from the National Oceanic and Atmospheric Administration can be found here.