When Fairfax County students return to school next Monday, they will find more work but also more reward for that work.

Administrators have been busy since school let out in June, and the major result of their labors has been a demand for significantly more work from high school students, particularly in math and science. The increased academic burden will be sweetened slightly by the creation of a "seal of distinction" to be affixed to diplomas of students with at least a B average.

"The point is to be sure the kids are prepared for college, to keep them in school all day, and to give them a rigorous program while they are there," said Elliott Krash, governmental relations specialist for the Fairfax County schools.

The more rigorous graduation standards, mandated for all Virginia's public schools by the Virginia Board of Education, technically take effect next year, but for the junior and senior high school students who want to deal with them most effectively, this year is the time to begin planning.

In addition to the stiffened course requirements, the 121,800 students scheduled to return to Fairfax schools when they open Monday will find a catalog of other changes, ranging from the first Reserve Officer Training Corps Program ever offered in the county to new salad bars at almost all the county's elementary schools.

The most significant changes:

In addition to stiffening high school graduation requirements, the Virginia Board of Education has created an "advanced studies" program for college-bound students. It requires them to take two additional year-long courses, as well as an additional year each of math and science and three years of a foreign language. That work will be rewarded with an "advanced studies" diploma at graduation. Students in the advanced studies program who maintain at least a B average will get a "governor's seal of special recognition" affixed to their diploma.

The county has banned all fund raising for outside charities by students during school hours, although students will still be permitted to collect clothes and food for the needy. Fund raising for school clubs and activities is unaffected.

A new program for gifted and talented students at the high school level will begin this year.

Herndon High School will offer the county's first-ever military training program, in the form of Navy ROTC classes taught by retired Navy captain Frederic Blakeman, who has been an American history and government teacher for the county for two years. The classes are elective, and only those who go to Herndon High can enroll.

Smoking has been banned from the campuses of seven additional high schools, bringing the total of no-smoking high schools to 14. The senior highs affected by the new ban are Fairfax, Langley, Madison, Mount Vernon, Oakton, Chantilly and Stuart.

For the third year in a row, the school system is not increasing the price of its lunches. Food services are increasing the range of offerings, most boldly at the elementary school level, where 95 of 123 schools will get salad bars.

"There is a lot of excitement. We expect this to be a real plus with the students," predicted Dorothy Pannell, director of food services. For those skeptical that an array of vegetables will excite elementary school students, Pannell offers that the salad bar "was tested last year and was a great success. And we found that elementary school students could handle a salad bar." The salad bar will cost elementary pupils 75 cents.

There will be milkshakes for the first time at the county's intermediate schools, for 55 cents, and Pannell promises "a few new menu items."

The numbers defining the nation's 10th largest school system are, in general, slightly smaller than those in last year's numerical profile. The anticipated enrollment of 121,800 is down 869 from last year. There will be 7,350 teachers, 50 fewer than last year.

And while this year's school system budget of $449 million budget is $23 million more than last year's, it grew a meager 5.5 percent, half last year's jump of 11.1 percent. "It is the smallest increase in the last 20 years," said Carl Juncker, director of the budget for the system. Juncker said the small increase is sufficient because teachers will get only 3 percent salary increases this year. He said the 5.5 percent increase was "adequate to run the system."

Two of Fairfax County's elementary schools will not reopen this year (Chapel Square and Wood), but three new elementary schools will debut (Cherry Run, Newington Forest and Oak Hill), increasing the number of schools in the system to 160 (117 elementary, 20 junior highs, 3 intermediate, 20 senior highs).

The most significant change for students, however, is the state's stiffer graduation requirements. Only this year's graduating class is unaffected by the new standards.

Beginning with the class of 1988 (which is in the eighth grade this year), all students will be required to take 20 year-long courses in high school to earn a diploma, two more the 18 currently required.

And those students will have to squeeze more than twice the amount of math and science into their four years of high school than have their predecessors. The regular (nonadvanced studies) diploma will require: four years of English; two years of math; two years of science; one more year of either math or science; three years of social studies; two years of health/physical education; and six electives.

Those requirements represent a jump of three years combined in math and science. (The old requirement was a year of each.)

Students who join the new advanced studies program will have to take 22 year-long classes, broken down as follows: four years of English; three years of math; three years of science; three years of social studies; three years of a foreign language; two years of health/physical education; and four electives.

The advanced studies diploma will first be available to those who graduate in June 1985--this year's high school juniors--but they must meet all the above requirements to qualify. Schedules are being adjusted for those who want to try for the diploma, Krash said.

"We already sent out a letter explaining the new program, and asking students to please let us know if they need to change their schedules so they can qualify if they so chose," she said.

The new advanced studies program does not have anything to do with, nor will it affect, advanced placement and honors classes that already exist at some high schools.

The increased class requirements, and their concentration in math and sciences, do create some logistical problems for the Fairfax schools, she said. "One problem is finding personnel to teach those courses. There is already a shortage of math and science teachers because they can get a lot better pay in business."

In addition to finding teachers, there is the problem of finding space for the classes. "We have calculated that when you add the additional science for the regular diploma students, we will need between 20 and 28 more labs, at a cost of $32,000 for each lab."

The problem is less severe for Fairfax County than for some other school districts, however, because many of the county's students already taken far more academic courses than have been required. "More than 50 percent of our children who go to college are already taking the courses they need" for the advanced studies diploma, Krash said. More than 80 percent of Fairfax's graduates go on to college.

The "seals of distinction" that will go on the diplomas of those who graduate with at least a B average also will be available beginning with the class of 1985. Those receiving a regular diploma will be awarded a "board of education seal of distinction."

Krash said it has not been decided whether all courses will be included in calculating the grade average, or just the 22 or 20 courses with the highest grades that also fulfill the graduation requirements.

The only other major program change for students is Herndon's experiment with a ROTC program. Herndon will offer Naval ROTC as an elective beginning this year. Already, 61 Herndon students have signed up for the course, including "a significant number of girls," according to Blakeman, who will teach it. He said he did not know the exact breakdown of men and women.