Teen-ager Tim Kissler, describing a calculus class at his high school, says it is tough to learn there when "for three weeks it's green, and then it's orange for three weeks, and then both greens and oranges come back for six weeks and the teacher has to review a lot."

Kissler, 17, "sounds like he's talking about a traffic light," according to his school friend, Warren Hoppe, 16, who knows better Hoppe is "a blue."

Both youths are students in Prince William County, a rapidly growing area in Northern Virginia and one of the last places in the nation where student bodies are divided into four student bodies are divided into four color-coded groups and attend classes on a year-round rotating schedule. One group or another is always on vacation while the other three are in school.

There is apressure lately to abandon the seven-year-old red, blue, green and orange groupings, and the county's school board, teachers, parents and students are suddenly caught up in a heated and complicated controversy over year-round versus traditional nine-month schooling.

The board, which is scheduled to decide the issue Wednesday, is finding that there is something to be said in favor of or against both systems. And therein lies the problem.

Among drawbacks to the year-round schedule -- where students attend classes for nine weeks and then have three weeks of vacation -- are these:

Steve Farmer, an English teacher and football coach at Woodbridge Senior High, is "on the red calendar" and his vacation breaks come in September, December, March and June. "I teach all July and August, and when my break comes in September, I have to be here every day to coach football."

Coaching duties are made even more difficult, Farmer said, because "every day there's a practice, one-fourth of the team is on vacation." If team members don't show for practice during their vacations, they don't play.

Phyllis Mosher, business teacher, finds that vacation breaks every nine weeks hurt a student's ability to retain skills. And, since surrounding school districts and most of the country are on traditional system, students trasnferring in or out of Prince William's program are disadvantaged.

"I got one from Faifax County recently who had 30 days of typing while my kids had about 75," Mosher said.

Students Kissler and Hoppe, a Woodbridge senior and junior, respectively,say those involved in extracurricular activities such as sports, band, choir or the student newspaper "don't really have a vacation at all" because these interests take up their vacation time.

The students like having four breaks a year but complain that the color-coded system tends to preselect their school friends since "you almost never mix with the other colors." Kissler, "a green," says the only reason he has a lot of "blues" as friends is because they all work together on the school yearbook.

Assistant Woodbridge principal Jerry Boling said the year-round system means "juggling courses and peopel to fit preferences like a big match game." Teachers don't get enough time with students outside the classroom, he complained, and he gets only one week at the end of a school term to plan for the start of another.

About 65 percent of Prince William's 37,935 students are in the year-round, color-coded groups, which began to be introduced in sectioons of the county in 1971 to cope with a student population that was growing faster than the county could provide facilities.

That enrollment is now expected to level off or decline over the next five years, and school superintendent Dr. William Helton -- citing teacher fatigue, poor summer attendance and scheduling difficulties -- has recommended to the board that the year-round system be phased out by 1981.

Students and parents surveyed by the county appear to be split 50-50 on the issue. Some who once howled in outrage against the year-round system now say they can't imagine conducting school any other way. They are used to it.

But 70 percent of the county's nearly 2,000 teachers wnt to return to the "summers off" system. They claim they are "exhausted" by the year-round schedule and often have to prepare separate lesson plans and tests for classes combining two or three color groups -- called "rainbow" classes.

The teachers also say the year-round schedule makes it hard to find time to take additional courses needed for master's or doctoral degrees.

There are, however, some notable exceptions.

"Four years ago when they talked about it for this school, it sounded like a wild, unworkable idea, but now I'm all for it," said John Brady enthusiastically. He is a journalism and English teacher at Woodbridge who is also adviser for the school newspaper, The Valkyrie.

Brady is one of Woodbridge's 75 or so extended contract teachers, which means he works 230 school days a year compared to 194 school days a year compared to 194 school days under the traditional teaching schedule. He is given two weeks off a year. The school has about 3,400 students and a faculty of 180.

"I heard a lot of warning about battle fatigue, but so far I haven't experienced it,' said Brady, who has worked the extended schedule for the past three years.

"The kids love it," said Brady of the year-round system. "They have four vactions a year, and they can come in on their breaks when needed and do nothing but their extra-curricular activity. I had a student who just went to Florida for three weeks in November to see her boyfriend."

Asked how he teaches and keeps track of his blue, green, red and orange students, Brady pulled four different colored pocket calendars out of his wallet. Teachers and students carry them around each term to help them remember the schedules.

Most of the academic classes are made up of "only one color," Brady said, but other teachers said it is not unusual to have a combination of colors if a school doesn't have enough of one color group to make up a class.

Teachers favoring the year-round system said it eliminates schoolwide tension or restlessness over coming vacations or tests and avoids the problem of everyone "holding their breath" in nticipation of June.

But social studies teacher Lee Miller, urging a return to the traditional teaching schedule, termed the year-round plan "an education failure" that adversely affects students and teachers alike.

"You always lose a couple of days [of classroom attentiveness] at the start and end of the term," said Miller. "Here, we do it four times, when in a normal year you would do it once."

Some county teachers, who make from $10,000 to $21,000 a year, depending on seniority and whether they earn an extended contract differential or $3,000 to $4,000, also complained that the year-round schedule prevents them from meeting for curriculum or program study.

Like the football team, the teachers also don't have a vacation or work period as a total group.

Superintendent Helton said studies commissioned by the school board offer no proof one way or the other about which scheduling system is better or more cost-effective.

"We have the capacity now to accommodate our student enrollment," Helton said. "For the first time since 1971 we have a choice."

The choice is actually up to the school board, whose seven members have received petitions on both sides of the issue and who are said to be largely undecided -- at least publicly -- about how they will vote.

Two members said they would not be surprised if the board ultimately decides to revert to the traditional schedule, but with a more gradual timetable than that recommended by the superintendent.

That would suit students Kissler and Hoppe and most of their friends just fine. Despite their criticisms of the year-round system, it's what they are used to and they would like to stay with it until graduation.

Lloyd Farley, a school guidance director, said the mechanics of scheduling and testing so mny different groups are horendous. "But if I was a student I'd look forward to those breaks, too. I'm in favor of the traditional system, but if I was on the board I don't know how I'd vote."