Wiley,
You are correct in your assumption. The USAF drew up, effectively, a JPITL for NVN which had IIRC 93 significant targets. These included POL, ports, LoCs, Dams and other infrastructure. The problem was two fold. Firstly, SAC had no real interest in playing and fought hard to prevent its' assets (not only bombers, but also tankers) being released. More importantly, RAND and Johnson were convinced that slowly knocking out targets, followed by bombing halts to encourage negotiation, the NVN government could be forced to desist ops in the South.
Some targets were just way off the reservation. The port facilities at Haiphong and the railways from China were verboten in case of hitting Russian/Chinese assets, and potentially widening the war. Hitting the dams would probably have starved large areas of the country - Johnson was terrified of world opinion if he did this. Invading NVN would have risked both.
By the time Nixon launched Linebacker, detente was in place and he could hit whatever he liked without the fear of widening the war, and he went after what was left of the target list. The NVN had to negotiate as they'd run out of SAMS and with the ports (finally) mined and the railways interdicted they couldn't replace them.