State transportation officials are seeking artists to contribute to the design of the first three new stations to be built as part of the Green Line Extension project. The state Department of Transportation and the MBTA are seeking to commission artists for a program to enhance the sense of place in key areas at the stations at Lechmere in Cambridge and at Union Square and Washington Street in Somerville. The concept is to provide art that has a unifying factor throughout the transit system while at the same time distinguishing the station platforms from one another, according to the Massachusetts Bay Transportation Authority. More information about the Green Line Extension art program and a request for qualifications can be found online at http://greenlineextension.eot.state.ma.us/arts_Program.html . Artists are also encouraged to participate in an informational session on Thursday at 5 p.m. at the Green Line Extension project office at 100 Summer St., Suite 250, in Boston. Artists interested in the program must submit their qualifications by Feb. 20 at noon.