Michigan congressmen, after a warning that the survival of the Detroit Free Press is at stake, said they may write a letter asking Atty. Gen. Edwin Meese III to approve a joint operating agreement with its rival. "I believe a good number of the delegation will sign a letter asking the attorney general to approve the JOA under these new circumstances that are so very final and definite," Rep. Dennis Hertel (D-Mich.) said after a private luncheon. The Free Press has lost $100 million since 1979. The JOA would allow the Free Press to merge business and printing operations with its rival, the Detroit News, while maintaining a separate news staff.