Thank you all for your replies. I realize how dangerous that situation was and need to do all I can to understand and correct this. To answer your questions:

My Bike is a Schwinn Super Sport, I think 1983 -- early 80s anyway. The brakes are Dia-Compe side pull and the pads are red material and marked "compe". They may be original with the bike but they seem to have plenty of rubber left. The levers are Dia-Compe and don't have the lever extensions. The rims are aluminum "Super Champion Gentleman 81" 36 spoke.

And the rear brake WAS out of adjustment. I could pull the lever all the way to the handlebar with one hand. That bad. I've tightened it up now. It seems that there's a lot of slack to be taken up in the long cable run. The front brake adjustment seems ok.

This hill is doesn't look so impressive when I look on a map. 7 or 8 percent for a quarter mile or so.

So what do I do. I guess I'll replace the pads with the best I can find, and make sure the brakes are adjusted correctly. I'll go out and practice locking up the rear brake to make sure I can do it and that I can handle the skid. And practice stopping short, though I don't want to dump the bike, or me.

As for hills, I can avoid this one, but I can't avoid them in general. Control the speed with the brakes all the way down if I might need to stop suddenly. The main thing is, I want to be able to trust my bike and I want to be able to trust myself on it.