Recent education changes aimed at high schools are being inappropriately applied to students in middle and junior high schools, a national principals' organization said yesterday, urging that younger students not be forced to specialize.

A report compiled by the National Association of Secondary School Principals also recommended that students in the fifth through ninth grades be given more guidance counseling and put in smaller classes. It also urged that teacher salaries be raised 25 percent.

The study focuses on the "middle level" years, when students are between 10 and 14 years old, a period that has received little attention among educators. A series of recent reports has criticized high school and college education in this country, but the NASSP said this is the first to study the middle grades.

"America has focused its attention on high schools for more than two years," said J. Howard Johnston, primary author of the report and dean of the College of Education at the University of Cincinnati. "The simple fact is, however, if students are messed up by the time they get to high school, it is unlikely they can succeed there."

In a series of recommendations, the report emphasized that students in junior high schools and middle schools should not be educated as if they were in elementary or high school.

"It is not an extension downward of high school education," said Scott D. Thomson, NASSP executive director.

The report did not suggest how the changes, some of which would require substantial funding increases, should be financed.

The authors call for changes in curriculum, teacher training and school climate. Among the recommendations:

* Educators should introduce these students, who are "interested in virtually everything, but nothing very much," to a variety of subjects and skills, without requiring them to master specific areas. If a school offers four foreign languages, for example, students should be exposed to each language for a short period, allowing them to concentrate on one language in high school.

* Teachers should deal with a maximum of 125 students a day. Many teachers now work with as many as 250. Also, teachers should be given training specifically for the middle grades and should not be asked to perform noninstructional duties.

* Schools should reward academic achievement as much as they do athletic and artistic achievement.

* Computers and other high-technology equipment should be integrated into the regular curriculum.