Depending upon the initial spacing, these trees may or may not "lose" foliage on their lower branches. Regardless, the tree's bottom branches simply do not "fall off" -- many conifers will only drop their photosynthetically active foliage (e.g., needles) due to low light conditions, high physiological maintenance costs, and density (i.e., light-enduced spatial competition from adjacent trees and canopy structure).
I certainly would not encourage you to "top" your white pine trees--topping is a cultural practice that is strongly discouraged!
I'm sorry I can't provide you with a better answer due to the simple fact that I am unaware of the spacing and size of these trees. If you require a more precise or immediate answer to your question, please contact a local urban forester, certified arborist, or ornamental horticulturist.
Best of luck!