I have a zoom 70 210, f 4. 5 /f 5 .6 , can I use it with a digital nikon 3100

It depends on the mount on the lens. If it has a Nikon mount then it will fit onto the D3100, though the camera's smaller sensor will make the lens seem more like a 105-315mm.

Since you didn't specify some details about the lens such as the maker, I can only speculate on the rest. Unless the lens has a focusing motor built in, you won't get autofocus. Also, unless the lens has compatible electronics, you won't get any exposure metering support from the camera and you'll have to use it in the manual exposure mode.