A Senate communications subcommittee debated turning the fairness doctrine into law Wednesday. The federal regulation, requiring radio and TV broadcasters to cover all sides of a controversial issues, was called unnecessary and probably unconstitutional by the Federal Communications Commission 1985. But the agency said it would continue to enforce the policy. Co-sponsoring the measure to write the fairness doctrine into law are Sens. Daniel Inouye (D-Hawaii), Ernest Hollings (D-S.C.) and John H. Danforth (R-Mo.).