The Board of Selectmen will conduct public interviews of the three finalists for town administrator at 6 p.m. Monday at Town Hall. The finalists, recommended by a search committee, are Robert Halpin, John Petrin, and Mark Stankiewicz. Halpin is president of the Newton-Needham Chamber of Commerce, and formerly was formerly town manager in North Andover and Westford, and president of the Merrimack Valley Economic Development Council. Petrin is town manager in Ashland. Stankiewicz is town manager in Plymouth. Halpin and Petrin are also finalists for the town manager post in Framingham. Following the interviews, the selectmen will discuss the candidates, and are expected to fill the position Monday or at the board’s next regular meeting, on April 9, according to Joanne Faust, the town’s human resources director. The three finalists were chosen from a field of 22 applicants. The search committee interviewed seven candidates. The new town administrator will replace Robert Mercier, who announced he will be retiring at the end of May.