Yes, the U.S. has a ‘space fence.’ As explained in this lengthy article by Brian Weeden, there is a considerably space surveillance network maintained by the U.S. Air Force, of which the space fence is a part. The whole system is focused on the thousands of objects in Earth orbit, and the fence is concerned with detecting breakups and collisions, while other parts simply track objects.
Weeden’s piece is extensive, but focuses more on how various Department of Defense officials are trying to preserve as much of the system as possible during the current budget climate. But the existence of this system makes me wonder if we have the seeds of a system that could do for the solar system what the space surveillance system currently does for the Earth.
Regrettably, my feeble recollection of orbital dynamics suggests such an expansion would require establishing a series of observation satellites not just in orbit around our planet, but across the solar system. Putting aside the logistics of such maneuvers, current Congressional arguments over whether we should retrieve an asteroid or not indicates we lack the political will to think that big.