Always a lot of essays to grade

''Learn to write'' is the watchword this year for high schools in Florida, where the state Legislature passed a $10 million Writing Skills Act last spring.

It is the first law in the nation to concentrate on the need of students from 10th to 12th grades to enhance their skills in all kinds of writing, from literary essays to job applications with essay questions.

Under the act English classes with writing components must meet the following three criteria: Classes may not have more than 25 students; teachers may not have a total teaching load of more than 100 students; each student must write no less than one paper a week.

The premise is thatreducing the classroom size and load will enable teachers to give needed one-on-one writing help. One hundred papers a week is still a lot , teachers say, but it's better than having up to 150 students, which makes the nurturing of good writing a nearly impossible task.

The program is not mandatory in the 67 school districts in the state. It does not create additional classes. It does, however, provide funds so that schools may have more units of the classes they now offer.

Each district submits its own plan according to need. For example, the Pinellas County School District, 24th largest in the country, is expanding upon the limited program it began last year under a less ambitious state statute.

Pinellas County will add a total of 33 English-writing units in 14 high schools. All 10th graders in the district will be in the writing program. All must take two classes, Grammar and Composition 10, and Literature 10, and all must write each week in these classes.

In addition, all Pinellas 11th graders will receive writing help in a required American literature course. And three electives will offer writing skills. For college preparatory students, there will be a writing course and a British literature course; for the district's best student writers, an advanced-placement English course.

The ultimate goal of the Pinellas district, located in the southeast St. Petersburg region, is to offer the writing-skills program to all 9th-through-12 th-grade students. All high schools have student newspapers and yearbook staffs, and most have literary magazines as part of an effort to encourage good writing.

''We have always stressed writing skills,'' says Dr. Margaret Howell, director of langauge arts for the Pinellas district, ''but this program will enable us to do an even better job. Our English-class load averaged 140 students. By reducing it to 100, our teachers can work in smaller classes and give students individual help, since they are not all at the same writing level.''

The 33 units added to the program have enabled some schools to retain English teachers whose jobs might otherwise have been terminated, because of drops in total school enrollment, she says.

''I am a strong believer that a good teacher of writing must be a good writer ,'' Dr. Howell says. ''We select our very best teachers for this program. Every summer we hold a workshop for 12 to 20 of these teachers, called Project Write, in which they develop their own writing skills.''

Will the writing skills program work?

''Our district has so much faith in it,'' Dr. Howell says, ''that when the state could only come up with $450,000 for the Pinellas district, our county district supplied the additional $221,000 so we could supply all 33 units which we needed. That's indicative of the enthusiasm we all feel.''