SUPPOSE A Hispanic child, speaking only Spanish, enters elementary school. Should he be taught to read in Spanish while he separately learns English? Or should he be taught only in English? One side of the debate argues that, if instruction is to be only in English, the Spanish-speaking child will fall behind while he learns it. The other holds that if he is taught in Spanish he will lag in his command of English.

The Reagan administration is moving, slowly, in the right direction on the highly inflammatory subject of bilingual education. The secretary of education, Terrel Bell, said last week that the federal government is now dropping the misguided rules it has been trying to impose since 1975. The department is no longer trying to tell local school districts they have to provide bilingual instruction--that is, instruction in the child's first language.

The administration is quite right. The country has now had quite a lot of experience with bilingual education, and, in most cases, such education falls in the large category of high-minded ideas that do not work well. Generally speaking, if these children are going to live and work in American society, they will be better served by being taught from the beginning in English.

The federal rules of the 1970s were formed under heavy pressure from Hispanic political and cultural organizations protesting that Spanish-speaking children had been neglected in the schools. In 1980, the Carter administration responded by proposing regulations greatly strengthening the bilingual requirement. That drew fierce opposition from, among others, the school systems of the Washington area with their very diverse populations of foreign- born children. It is not unusual to find classroms here in which a dozen languages are represented, including those of the Vietnamese hill tribes. To teach these children in their own languages is hardly possible. Now Secretary Bell has taken the important step of stating that the federal government will not require the bilingual principle.

If a child comes into an American school knowing little English, he has a right to special help. That right has been affirmed by the Supreme Court, and no one disputes it. The argument is over the form it ought to take. Some school systems prefer bilingual instruction, and they will stick with it. Others employ, instead, intensive instruction in English. The federal government has a responsibility to see that children get the attention to which they are entitled. But it has no business doing what the past two administrations tried to do-- tell local school systems precisely which method they must follow and how they must follow it.