BOSTON — The UMass board of trustees moved a step closer this week toward freezing tuition and fees for students for a second straight year. The board’s finance committee voted unanimously Wednesday to hold the line on costs. One June 18, the full board is scheduled to meet at UMass Dartmouth to take up the matter, according to a statement from the university. The freeze is contingent on the Legislature maintaining its spending level for the university system. Under the proposed freeze, tuition and fees for in-state undergraduate students at UMass Amherst, the most expensive undergraduate campus, would remain at $13,258, not including room and board.