President Reagan, who is rapidly becoming one of the nation's best known education experts, went to Kansas on Wednesday and unleashed his latest pet theory on what caused the crisis in America's schools. It's all the fault of the courts.

This leap from the bench to the classroom took place in the following fashion: according to President Reagan, the system started going downhill 20 years ago when the courts started requiring schools to take the lead in correcting "long-standing injustices in our society: racial segregation, sex discrimination, lack of opportunity for the handicapped.

"Perhaps," Reagan told a student group, "there was simply too much to do in too little time, even for the most dedicated teachers and administrators. But there is no question that somewhere along the line, many schools lost sight of their main purpose. Giving our students the quality teaching they need and deserve took a back seat to other objectives."

There is a great deal to be said for President Reagan's current interest in education, but he is showing signs that he needs a better briefing book.

Up until a couple of decades ago, education did, indeed, focus on white males. Far more white males went to college than did white females or blacks or handicapped youngsters. But a change of national purpose occurred: decisions were made in Congress, in the federal government and in the courts as well as in communities across the nation to provide equality in education to everyone, not a superior education to some.

The mandate was accompanied, over the years, by huge expenditures of federal funds to help educate children who couldn't speak English, children bound to wheelchairs, children who were learning disabled, and Indian children, and by spending some money to expand the educational and professional horizons for young women. This is hardly a cause for criticism.

Unlike the president, the American public does not seem to feel that education has suffered as a result of broadening access to it. The 14th annual Gallup poll of the public's attitudes towards schools, published in Phi Delta Kappan magazine last September, found that lack of discipline, not diversity of the student body, remains the number one concern, followed by insufficient financial support, use of drugs, poor curriculum and standards, and difficulties getting good teachers. Only 6 percent of those polled cited integration and busing as problems, and only 1 percent cited non-English speaking students and government interference as problems.

There is no reason to believe the job of providing equity in education to all educable youngsters is over. Both in its actions and rhetoric, however, the Reagan administration raises questions as to whether it remains committed to the goal. The administration tried to zero-fund the women's educational equity act program, and failing that, put a New Right activist in charge of it. The administration is about to conduct a reduction in force and to downgrade jobs in programs that promote educational equity for women and minorities. "They want us back in the closet and in the kitchen rather than in the public schools educating ourselves so we can be meaningful members of society," charges Pat Reuss, executive director of the Women's Equity Action League.

President Reagan is on tour these days promoting a back-to-basics view of education. Given what is going on in the education department, and his snipes at the role of the courts and the federal government in education, one has to wonder just what he means by a return to basics. What will be sacrificed in the rush to produce more mathematicians?

Two weeks ago, President Reagan told a national PTA convention to "send a message to Washington . . . that you want the basics in your schools and the parents back in charge. Tell them education must never become a political football because your children come first . . . ."

Thanks to the president, education has become the biggest political football around. On the road back to basics, however, it is well worth remembering that parents with lots of different kinds of kids have gotten used to thinking their children come first.

They won't want to see them kicked in the teeth.