Many factors both biotic and abiotic can cause brown needles on white pine. The most common thing is the natural browning, and dropping, of the older, inner needles. Needles that are 4-6 years old will yellow, then brown and drop in the fall. It is normal for pines to drop their oldest needles in the fall. This annual shedding occurs on all pine trees at about the same time, and always occurs in the fall. If this is the case for your tree, there is nothing for you to do. Just give the tree 'good care' by mulching and watering. It is abnormal for needle drop to occur in the spring or summer..
Poor root zone conditions can cause pines to lose needles early. Watch for compacted soil, standing water or flooding, cutting major roots, parking vehicles on the roots, etc.
De-icing salt injury may cause the death of white pine needles and branches. Symptoms from salt injury show up on the side of the tree closest to the salted road. Trees closest to the road are most severely injured.
If you wish to get a definitive diagnosis for a fee please send a sample to the Plant Disease Clinic at the University:
http://pdc.umn.edu/

 There are needle blights that can affect white pine- here is a link to an article about blight. It was written for Christmas tree farmers, but the disease symptoms can be compared to your situation http://msue.anr.msu.edu/news/managing_dothistroma_and_brown_needle_blight_on_pines

You can consult a certified arborist, who will come on site, evaluate the tree as a whole, and give a diagnosis and a plant heath care guide.