CLEVELAND, Ohio (AP)—U.S. District Judge Robert Krupansky has ruled that women who have been fired solely because they became pregnant cannot be denied unemployment compensation William Papier, director of resarch of the Ohio Bureau of Employment Services, says the Tuesday decision will cost the state at least $300,000 a year Unemployment benefits have been denied employer discharged because of pregnancy. Judge Krupansky's order is retroactive to Oct. 22, 1972. That is the day Edythe Lasko, the Fairview Park woman who challenged the denial, would have been eligible for benefits. Mrs. Lasko, 24, a secretary receptionist, was discharged in Oc tober about two weeks after she told her supervisor she was four months pregnant. She filed a class action suit in December against the Bureau of Employment Services on behalf of all women fired because of pregnancy but still able to work. The suit was handled by the Women's Law Fund, which asked for a three-judge panel to declare the pregnancy section of the Unemployment Compensation Act unconstitutional. U.S. Appellate Judge Paul C. Weick, Senior U. S. District Judge Girard Kalbfleisch and Krupansky decided that the law itself was not un constitutional but that the state had applied it in an unconstitutional way. They ruled in an order filed Tuesday that the case for damages would be properly handled by one judge.