Delta Air Lines Inc. offered its 13,000 pilots a raise of about 27 percent over four years, significantly less than what the employees have proposed in contract talks that have lingered since the beginning of the year. The carrier’s proposal was disclosed in a letter Sunday to pilots from John Malone, chairman of the Delta chapter of the Air Line Pilots Association, which is asking for a 37 percent raise over three years. The two sides have been deadlocked over pay and other issues since the contract became amendable Dec. 31. The union has taken an aggressive stance in negotiations with the Atlanta-based airline, saying that the carrier’s profits justify the reversal of pay and benefits cuts adopted in the early 2000s. The pilots had voted down an agreement in July 2015 that would have provided an immediate 8 percent raise and smaller boosts in future years. “Delta is committed to reaching a timely new agreement that is market-based, sustainable, and that also ensures Delta pilots have an industry-leading package of pay, benefits and work rules,” Morgan Durrant, a spokesman for the airline, said in an e-mail. An ALPA spokeswoman didn’t immediately return a call or e-mail Monday. The pilots and Delta began mediated talks under the supervision of the National Mediation Board on March 31. The agency suspended the talks for three weeks early this month, suggesting the NMB believed progress toward a deal had “stalled,” Malone wrote in an earlier letter to union members.