The premise seems simple enough: Want to make students learn more? Keep them in school longer.

But efforts to do just that in Fairfax County have brought loud protests from teachers and parents in the last year. Last November, the School Board sparked a fierce backlash when it extended the secondary school day by 30 minutes, and on Thursday it risks a repeat when it votes on a plan to eliminate the practice of closing elementary schools early on Mondays.

If it approves the latest plan, Fairfax will have accomplished something few school districts in the nation have: Students in every grade will spend the equivalent of three more weeks in school each year.

But teachers are unimpressed. By taking away their time for joint planning conferences on Monday afternoons, they predict the quality of education will go down, not up.

The Fairfax dilemma represents a case study of how two well-intentioned educational goals can collide head-on: More instructional time for students vs. more planning time for teachers.

Few are happy with the Monday extension proposal by Superintendent Robert R. Spillane. Two teacher unions plan to rally more than 500 of their members at Thursday's meeting. County politicians have criticized the $5.6 million price tag of the Monday extension. Parents have been lukewarm at best and many are expected to testify at a public hearing tomorrow night.

Under the plan recommended by Spillane, Fairfax would have a uniform 6 1/2-hour elementary school day next September, equal to that in Howard and Loudoun counties and half an hour longer than the school day in Alexandria, the District and the counties of Montgomery, Prince George's and Anne Arundel. Arlington and Prince William have schedules like the one Fairfax is trying to change -- four 6 1/2-hour days and one early closing each week, averaging out to six hours a day.

Under Spillane's plan, teachers would have planning time scattered throughout the week during times when their students take physical education, art and music classes. Those subjects, often the classroom teacher's responsibility, would be taught by special teachers hired for the purpose.

"I may have a half an hour here and a half-hour there but if I actually need to make phone calls or sit down with the other kindergarten teachers, you can't do it," said Sarah Walker, a kindergarten teacher at Hayfield Elementary School. "You need a big block of time to coordinate what you're going to do."

At Hayfield Elementary, south of Alexandria, teachers spent a recent Monday afternoon conferring about troubled students, planning joint science lessons, telephoning parents and scheduling time for tutoring.

With the uniform 6 1/2-hour day, they said they fear they will not have the same planning period to consult with one another.

"It's almost impossible now," said Jennifer Logan, a special education teacher who must collaborate with teachers in several different grades. "And it's going to be worse next year" if Monday is extended.

Other jurisdictions have operated without early closings for years. Teachers in some of those schools, however, said they have long eyed their Fairfax counterparts jealously.

"Fairfax has been the envy of teachers here because that Monday afternoon is really needed," said Mark Simon, president of the Montgomery County Education Association.

Fairfax began closing its elementary schools early on Mondays about 20 years ago to give teachers an uninterrupted block of time for planning, professional meetings and parent conferences.

Several years ago, school officials concerned about the lack of after-school day care began contemplating an end to the practice. But after garnering little support from parents, they shifted their rationale to instructional benefits. A 1983 report on the country's schools, "A Nation at Risk," recommended lengthening the school day for all children to improve academic performance.

"American kids spend less time in school than anybody else in the industrial world," Chester E. Finn Jr., a former Reagan administration education official, said recently in an interview. "They do less homework. They watch more TV . . . . Then why are we surprised when they fare poorly in international comparisons?"

Though some families use Monday afternoons for children's ballet lessons, band practices and soccer games, some youngsters are latchkey children for that one day each week. In a few highly publicized cases, children have been injured or killed in accidents on Monday afternoons.

"To me, {early closing} makes no sense," said Helen Garamone, mother of a first-grader at Fort Hunt Elementary School. "I see kids on Monday afternoons just hanging around, wasting the time . . . . The time should be put to their advantage."

"It seems to me to be a very logical step," said Margaret A. Marston, a former member of the Virginia Board of Education who was on the panel that issued the "Nation At Risk" report. "More time in school with a teacher working with students should certainly give you a sounder student."

Still, although parents may seem like natural supporters of the Monday extension, many have remained quiet or come out against the plan because of its impact on teachers and the budget.

"The parents are in a quandary," said School Board Vice Chairman Laura I. McDowall (Annandale), a strong supporter of the plan. "They believe this is good for kids, but they don't want to go against the teachers."

In Fairfax, a poll commissioned by the School Board last spring found that 49 percent of county residents surveyed opposed extending the elementary school day, compared with 43 percent who supported it. Among parents of elementary schoolchildren, the gap widened, with 59 percent against and 41 percent in favor.

Educators share that ambivalence. Some say there's a fine line between squeezing as much out of a day as possible and pushing students so far that their productivity actually goes down.

"It's almost a toss of the coin," said Harry Bibb, associate superintendent of schools in Loudoun County. "How productive are youngsters going to be in school for 7 1/2 hours or eight hours? That's the question."

IN HOURS

School District......Elementary School....Middle School....High School

Alexandria...............6....................6 1/2............6 1/2

Arlington County.........6 ...................6 1/2............6 1/2

Fairfax County...........6 1/2 ..................7.............7

Loudoun County...........6 1/2...................6 1/2............6 1/2

Prince William County....6 ...................6 1/2............6 1/2

District.................6....................6.............6

Anne Arundel County......6....................6-6 1/2..........6 1/2

Howard County............6 1/2...................6 1/2............6 1/2

Montgomery County........6....................6 1/2............6 1/2

Pr. George's County......6....................6 1/2............6 1/2

Note:Hours are rounded to the half-hour and exact hours vary by school. Some specialized magnet schools have longer hours (Jefferson Science and Tech in Fairfax has a 7 1/2-hour day and the Duke Ellington School for the Arts in the District has an 8 1/2-hour day).

Have four 6 1/2 hour days and close 2 1/2 hours early one day each week, averaging out to 6 hours a day.

As proposed in Fairfax. Current schedule is the same as Prince William and Arlington.

SOURCES: Area schools.