To the best of my knowledge, clear film finishes, like lacquer, varnish (including polyurethane) and shellec would not have lead. Colored paints, and particularly enamel paint that is from prior to 1972, probably does have lead in it. You can get test kits at home centers now that will tell you quickly if lead is present. With the cost of the chemicals for paint stripping, it seems like this would be money well spent.
For what it's worth, I would not bother stripping or testing if I had a clear film floor to deal with.