After three relatively placid year, the Arlington School Board is bracing itself for the uproar that is likely to accompany a forthcoming study of secondary school reorganization.

On top of all the other problems the school board will confront this year -- most of which are financial in nature -- school reorganization promises to be the most volatile because, inevitably, it will involve future school closings.

Whatever plan is finally approved, it won't be implemented until the 1983-84 school year, but its outline will take shape this year.

The reorganization, which will cover grades 7 through 12, eventually will have an impact on everything from football to curriculum changes to teacher layoffs.

The new reorganization study was prompted by declining enrollment, which has been shrinking at a yearly rate of nearly 5 percent in Arlington for the past few years. This year's projected enrollment at 31 schools and education centers is 14,338, or 564 fewer students than last June.

The last major review of secondary schools was in 1977-78. It resulted in the closing of Stratford and Gunston junior highs and in a reorganization that switched the school system from a junior high-senior high format to an intermediate-senior high grouping by transferring 9th graders from junior highs to senior highs.

In an effort to attract as much citizen participation as possible, the school board last spring appointed a 28-member commission of educators and parents to begin the study. Its first preliminary report to the board is due Oct. 1.

"It will be an inventory of what we have now and a look ahead at the numbers and problems and challenges we face," said Donn R. Marston, chairman of the commission. "We're going to take as comprehensive a look as possible at the system.

"If this (study) were simply another exercise on how you shrink the system, it would be a negative (approach). The challenge is to look ahead at the kind of system Arlington wants and then look at the options of how you get there."

The commission hopes to produce a preliminary report on possible changes by Jan. 1 and plans to give the school board its final report and recommendations by May 1. The board is expected to hold extensive public hearings before making its decisions next summer or fall. It would take another year to implement the plan, by current estimates.

For the purpose of its study, the commission has created committees covering course offerings and staffing, extracurricular activities, special student services and facilities and transportation, Marston said.

It is possible that the commission will recommend no school closings, but it is too early to make any predictions, he said.

The school board's other major challenges during the coming year will be budgetary, caused largely by cuts in federal aid and a continuing desire by the County Board to tighten the belt on school spending.

As it heads into the new school year, the board has a new superintendent, Charles E. Nunley, who has developed a reputation in educational circles as a fiscal conservative. The board will also have two new members -- Simone (Sim) J. Pace, also a fiscal conservative, and a member who will be appointed in late September to fill the unexpired 22-month term of O.U. Johansen, who is retiring Sept. 1.