Ohio's troubled school financing system was ruled unconstitutional yesterday, but the judge said he would delay implementation of the ruling until next summer.

"This court is compelled, in view of sheer weight of evidence, to find for the plaintiffs on constitutional grounds." Judge Paul Riley said in his Hamilton County Pleas Court decision. The Cincinnati school district, in a class-action suit, had argued that the state legislature's funding system failed to abide by the Ohio constitutional requirement to provide a "thorough and efficent education."

The year-old financing system makes state funds contingent upon the ability of local districts to pass tax levies. The Cincinnati suit contended there was a gross disparity in per-pupil funding among different districts because of varying local tax bases and the willingness of property owners to approve tax levies.

John Lloyd Jr., attorney for the schools, said the disparity of state funding to local school districts also violated equal protection clauses of the law.

"Realizing that the state funds are essential to the operation of the districts. I am ordering this decision to take effect July 1, 1978," Riley said at the end of the year-long trial.

The judge's decision to implement his order next July 1, the start of the new fiscal year, will allow school districts to remain open and the state legislature to come up with a new method of financing their operation.