Four teens saw bright light only a few hundred feet in early evening sky for about 15 minutes, no noise!

In the fall of '72 or '73, myself and 3 other friends were walking (nobody had a car yet) around in the cool early evening seeing what kind of trouble we could get ourselves into (we were 15 or 16 year old high school students).  We ended up playing around the northbound and southbound rt. 690 bridges over the Seneca river, just outside of the village of Baldwinsville, N.Y..
I guess that we irritated a motorist or two while fooling around.  One of us noticed what he thought was a police helicopter looking for us with a spotlight.  We quickly hid under one of the bridges trying to avoid being spotted by the chopper and it's light.  We kept looking out around the bridge girders trying to see what the helicopter was doing when someone else noticed that there was NO helicopter sound at all.  It was entirely silent although we figured it to be only a few hundred feet above us.  I also noticed that there was no traffic anymore although previously it was relatively steady.  We started to get scared as the spotlight continued, we thought, looking for us.
 As we were trying to figure out what to do next, it was like the light and craft (?) got tired of looking for us and it started to slowly move towards the village, over the river, and shining its light to the left bank, then the right bank, then left, then right, and kept repeating that maneuver 'till it disappeared.  As soon as it was out of sight, the traffic started appearing again!  
We were all quite scared and bewildered and left the area immediately!  
Other than between ourselves, we heard nothing of the incident from anyone else (apparently, no one had reported anything).
Witness indicates that the date in September 1973 is approximate.  PD