The Malden Redevelopment Authority , National Grid, and developer Alex Bok have reached agreement on the terms of a 40-year lease to build a $50 million minor league baseball stadium on the site of a former gas distribution facility on Commercial Street.

A letter of intent outlining key terms of the lease, such as rent payment to the authority, must be approved by the state attorney general’s office before a final lease is signed. “We’re cautiously optimistic the attorney general will approve the proposal,” said Stephen Wishoski, executive director of the authority.