EDF Energy wants to build a new plant - Sizewell C - on the coast.
Villagers on the A12 want a bypass to keep construction traffic away from their homes.
Suffolk County Council has agreed to spend the money on further studies to create a funding case to present to the government.
EDF has said it aims to build Sizewell C in the 2020s at a cost estimated to be about £2bn.
The villages which would be by-passed are Marlesford, Little Glemham, Stratford St Andrew and Farnham.
The council said a new section of the A12 would take up to two years to build and cost between £45m and £105m depending on how many villages were bypassed and whether the road was single or dual carriageway.
EDF has estimated traffic on the A12 would increase by about 14% at peak times and the council has identified a bypass as one of its strategic transport improvements.
James Finch, Conservative councillor with responsibility for transport, said: "The environmental impact is important, so that needs to be taken into account and all the necessary studies done to protect that environment."
The authority said it would look to EDF to contribute to the costs.
EDF has no firm timetable for building the nuclear plant and has yet to make any commitments to funding a bypass.
A council has agreed to spend £450,000 on a study which could see four villages bypassed ahead of a planned new nuclear power station in Suffolk.