"I'm not sure if it's cast iron - could be lead?"

Lead was used for supply pipes and DWV lines, but not steam lines.

A good plumber should be able to drill the hole larger and tap it for a plug.

A less skilled plumber will try to cut out the section and replace it with two nipples and a union.

It is more likely that it is seamless black iron pipe.

Go to a heating contractor supply house and they have a special "Pipe Repair Clamp" made for this purpose.

The repair clamps have two pieces that are formed into a hollow channel to surround the pipe. One side of the clamp is held together in the same manner as a butt hinge and there is a flat neoprene gasket material on the inside of the hollow channel. The clamp is opened like a clam shell, slipped over the leak then folded closed and held in place by two small bolts on the open side.

I would not put a pipe repair clamp on a steam line.

212F steam is going to harden up the gasket material in short order.

what about pipe repair wrap? One made by Fernco was suggested. Would that be a good solution if we didn't want to cut out and replace the pipe at this time?

The pipe repair clamps sold at home supply centers are not suitable, neither is the wrap.

Go to a real heating contractor supply store and they have repair clamps that are rated for high pressure steam that are ASTM certified for up to 400degF.

" Would that be a good solution if we didn't want to cut out and replace the pipe at this time?"

Drill and tap the hole and install a machine screw or plug.