Hi, Mary. Now we can direct people who want to fill and paint their paneling to somebody with experience with the problems that happen down the road. I suspect that your problems will only get worse.
There is a fiberglass product that you can put on your walls with a heavy paint that will consolidate the lose material in the cracks. It does work very well but is expensive. The second long-term answer is for you to remove the paneling, hope that there is drywall in pretty good condition underneath, fill the holes and paint that.
A primer is generally a lighter version of the same kind of paint. They are made to soak down in the surface you are painting so you have a good base for the paint. You might have some luck with a shellac based product like Zinnser's B-I-N filling small cracks but the stuff in the cracks will always want to work its way off. If you do fill with a paintable latex caulk, that too will work for a while but I think that you will still have future problems in other areas.
Good luck and sorry that I don't have an easier answer for you.