The lines being examined closed to passengers in the 1960s
Passenger lines axed from the rail network under the Beeching reforms in the 1960s could once again see trains.
The Welsh Assembly Government has asked Network Rail to conduct feasibility studies on two former track stretches.
The lines are on old sections between Llangefni on Anglesey and Bangor, and between Aberdare and Hirwaun in the Cynon valley in south Wales.
In both cases, while the routes were closed, the disused rail tracks still remain in place.
"This could provide an economic stimulus for Anglesey and further proposals to extend passenger traffic between Llangefni and Amlwch," responded the leader of Anglesey council, Coun Clive McGregor.
"We support the concept and would be prepare to play our part in facilitating the process.
"I have personally received a number of positive comments from members of the public who visit the Island that a steam heritage railway would be a major tourist attraction for Anglesey."
The decision to commission a feasibility study was revealed by the Deputy First Minister, Ieuan Wyn Jones, as he addressed the assembly's enterprise and learning committee in October.
He said the two sections of line were of particular interest, because the tracks had not been ripped up when original passenger services closed.
"What we are doing here is, rather than thinking - at present, anyway - about areas where the track has been removed, we are looking at areas where the track is still in place and it is easier to introduce new services," the minister said.
"There may be other areas in Wales where we might feel, at some point, that it is worth looking at such services, where a track is in existence but where there are no services."
The original Llangefni rail station was part of the Anglesey central line running from Gaerwen to Amlwch on the island, dating back to the 1860s.
It was closed to passenger services in 1964 as part of the massive cuts imposed by the Beeching review of rail transport, though continued to operate as a freight stop until the 1990s.
Like Llangefni, Hirwaun also fell victim to the Beeching axe. But it too maintained a freight role, carrying coal from Tower Colliery.
Network Rail has already began work on gathering evidence for its study, beginning with cutting away vegetation on track sections to examine the condition of rails and track bedding.
Its report is expected to be published next year, before any business cases to reopen the lines are then developed.