The plan to extend PATH to Plainfield was mostly an NJDOT plan. The plan was announced by Gov. William Cahill on Nov. 15, 1972. It was part of a package of rail projects in New York and New Jersey to be financed with $650 million in Port Authority funds. This was reported in newspapers on Nov. 16, 1972 throughout the Metropolitan Area. In addition to extending PATH to Plainfield, money was also supposed to go to getting EL into Penn Station.
However, PA financing would've required bi-state legislation amending the 1962 PA bond covenant and was certain to trigger bondholders' suits. Critics saw no chance of the bondholders losing those suits. By the following year, 1973, the PA was seeking $150 million in US funds to cover two-thirds the cost of the extension. However, US DOT said no.
When Brendan Byrne was elected Governor there was a renewed effort to get the PATH extension. Byrne actively lobbied to get US DOT to reconsider. I think it was at this point, with Conrail looming on the horizon and agreeing to takeover the CNJ service, that NJ DOT began to feel it was no longer a pressing matter.