The state announced a land-swap Thursday that paves the way for a new Lechmere Station and the Green Line Extension into Somerville and Medford.

Lechmere will be relocated to the former Pan Am rail yard across the street from the current station. In exchange for giving MassDOT property rights crucial to building the Green Line Extension, Pan Am Railways will acquire the existing Lechmere property.

The new station will be built as part of a long-delayed mixed-use development called NorthPoint, whose original developers pledged to pay $70 million to rebuild Lechmere Station. That pledge was made before the Green Line Extension proposal, which will surely increase its price tag.

Under the current agreement, MassDOT receives $36.6 million worth of land and track rights plus $21.5 million for other incidentals.

Also, the land under the current T station was assessed at $32 million in 2006 and is currently believed to be worth considerably less.

“The successful relocation of Lechmere Station is key to the extension of the Green Line,” MBTA General Manager Rich Davey said.