PORTLAND – The publisher of the Portland Press Herald has asked a federal judge to decide whether a buyer of the newspaper is obligated to honor its union contract.

Blethen Maine Newspapers sued the Portland Newspaper Guild, saying its refusal to allow the issue to go to arbitration has had a chilling effect on the company’s efforts to sell its newspapers.

In a complaint filed Tuesday, Blethen Maine said it has already cut costs and needs to sell its assets to reduce debt and avoid default. But the Guild says the company is required under the 2007 contract to make sure that its terms are assumed by a purchaser as a condition of any sale.

The lawsuit comes three months after the Seattle Times Co. announced that it was putting its daily newspapers in Portland, Augusta and Waterville up for sale. Since then, there have been two rounds of job cuts aimed at offsetting growing costs of energy and newsprint and a drop in advertising revenue.

In an e-mail to newspaper employees, Publisher Chuck Cochrane said of the lawsuit, “The company reluctantly took this step only after repeated attempts failed to convince the Guild’s leadership to voluntarily agree to resolve this matter through an expedited arbitration.”

The union contract, which expires in 2011, states that the agreement “shall inure to the benefit of and be binding upon the successors and assigns of the Publisher.”

Before filing the lawsuit, the company met twice with Guild leaders to discuss the dispute, but did not get the sense that the Guild wanted to resolve the issue in a timely manner, Cochrane said.

“Even though the owners of Blethen Maine Newspapers do not believe that a buyer can be forced to assume the Guild contract,” Cochrane’s e-mail continued, “they are willing to ask prospective buyers if they will agree to do so voluntarily. However, none of the interested parties has so far indicated any inclination to accept the current contract as it is written.”