IF YOU HOPE to go to college next year, you will have to give up a Saturday morning, take a number two pencil and, with the eraser end, break the seal on the Scholastic Aptitude Test. Then after answering two-and-one-half hours of questions on such topics as the mean height of an adolescient basketball team and the antonym of "schism," you'll end up with a score somewhere between 200 and 800 each for the math and verbal sections. These numbers could make the difference between receiving fat letters from college admissions departments (Yes, we want you) or skinny letters (While we had many fine applicants . . .) Beat the System

The SAT doesn't have to be an inevitable monster over which you have no control. There are students who, between taking the PSAT (Preliminary Scholastic Aptitude Test given in the junior year) and the SAT the following year, and, in effect, 100 points to their math or verbal scores. The Educational Testing Service, which develops and administers the exam, says one teenager in twenty may make such a gain.

Some experts believe the mystique and awesomeness of the tests intimidates students so that their scores suffer. An ETS staffer recalls that when she was in high school, the SAT was "a do-or-die thing." But consider these facts before you get all jittery:

A sixty-point difference between two students - one, for example, with a 470 and another with 530 - may be "insignificant" according to the ETS. Jim Braswell, test development coordinator, says that a student's "real" score can be thirty points more or less than what shows up on the card. (Colleges are warned about this deviation. Just hope they listen.)

According to the latest figures, fifty-four per cent of college-bound seniors taking SATs score between 400 and 600. The average verbal score is around 435. In the math section, fifty-eight per cent of the test takers score between 500 and 600. Average is around 480.

Scores will vary for students taking an ETS exam more than once. The typical gain, according to ETS, between a PSAT and SAT is twenty-four points for the verbal section and eighteen points for the math. Students sitting for the SAT twice will normally register a twenty point gain.

If you're shooting for the moon, you should know that it's easier to rack up a prefect score on the math section. Out of 840,000 students who recently took the SAT, 99 received an 800 score on the verbal section and 716 earned a perfect 800 for math.

Guessing, according to ETS, "probably won't affect your scores significantly." On the other hand, leaving questions blank won't help you very much because the test is scored by subtracting a fraction of the number of wrong answers from the total number of right answers, and unanswered questions are not figured into the scoring. Generally, if you have even an inkling about a question, and can eliminate one or two of the multiple choices, guessing could well give you a right answer and improve your score.

The SAT is not put together by dusty academicians whose favorite books are the unabridged Oxford English Dictionary and The Decline and Fall of the Roman Empire. To day's tests were devised more than fifty years ago by a Princeton psychologist, Carl Bingham. Bingham was responsible for dividing them into math and verbal sections, for using a 200 to 800 score (he wanted to get away from the traditional 0-100 system so edcuators wouldn't think in terms of pass or fail but instead compare students' scores), for the secrecy surrounding SATs (tests are never made public), and for insisting on the multiple choice format.

Pam Chambers, a 27-year-old graduate of Trenton State College with a B.A. in English literature, is an ETS assistant examiner who writes SAT verbal questions. She puts them together the same way Bingham did. She finds a word from novels she's reading at home, or magazines or textbooks at ETS. Next, she checks the "item files" to make sure it hasn't been used before. If she's writing an antonym question, she looks up the word and its opposite in Webster's New International Dictionary, Second Edition. Her next step is to think up "distractors" - the other choices in a question that will sort out the dull students from the smart from the very bright. Generally, each multiple choice question includes an obvious wrong answer, a couple of possibilities that just could be right, one choice that is very similar to the answer, and the right answer.

Pam applies basic principles of multiple-choice testing to her questions: never make the right answer longer or shorter than the distractors, don't use tip-off words like "always" or "never," and make sure a word is used only once in a test.

It may ease your mind to know that one-fifth of your SAT will not count toward your score. Every SAT contains two verbal sections, two math sections and a fifth part which could be either. This fifth section is composed of experimental questions that ETS is testing and analyzing before they become permanent SAT items. ETS hopes candidates can't tell the difference between the experimental section and the others, but who knows?

Knowing how the system works may not ease your mind enough to add 100 points to either the math or verbal. The pressure mounts, as Pam explains. "There's no big difference between thirty points on the SAT. But it can be a big deal if you want to go to a college with a cut-off point of 1000 [combined math and verbal figures] and you have 970." So, for insurance's sake, here are some other ways to boost your score. Buy the Points

Scattered around Washington are "coaching" schools that specialize in priming students for the SAT. Although ETS says coaching doesn't help (It suggests studying only if a student has been away from math for more than a year), these schools can turn out students whose total math and verbal scores improve by 100 points. The Stanley Kaplan Educational Center calls this kind of gain "very, very common."

None of them offer magic formulas. The Heights Study Center guarantees, money-back, that its course will add 100 points to a student's combined score if the student attends all classes and completes all homework assignments.Most schools, however, don't really know how much their students' scores improve because they don't hear from them after the exam. Only in cases of people claiming their money back, or when they're estatic about a 200 point increase is there any feedback.

Coaching courses last anywhere from three to ten weeks, totaling twenty to forty hours of class time plus a couple of hours of homework every week. Costs range between $95 and $250. Classes are spent taking sample tests and reviewing fundamentals.

Teaching the art of test-taking is one of the basic purposes of these schools. "Students are stymied more by the format than the content," says a teacher at Prep Courses. "We teach them how to budget their time, how to eliminate the obvious wrong answers." Another school, Transemantics, works to make testing as routine as brushing teeth. Says Heights Study Center, "We teach them the techniques. Some kids have to learn how to skip questions and do less guessing. Others should eliminate and guess more."

These schools generally use their own books and resources instead of commercially available tests. Some also offer lectures on cassettes for students who miss classes or want to review. Most of the sample tests are developed by the schools' teachers. No one has access to actual SAT examinations, only to sample questions published in ETS's explanatory booklet sent to candidates. However, the sample tests are as important for form as for content. Even ETS admits that familiarizing students with the layout and the kinds of questions presented may ease their nervousness.

The school's programs typify the different approaches to SAT. The Heights Study Center is big on drills for vocabulary and math problems: "Repetition is the mother of learning," says one of its teachers. To prepare students for the SAT-verbal, it emphasizes vocabulary. "Vocabulary studies are not the panacea for a good score but they are the single most important area for improvement." The biggest problem in the math section is the student's failure to read the instructions. "We've found that most math mistakes are from misreading the question."

Transemantics in downtown Washington figures that if any student's score for either the math or verbal section increases by fifty points, it has contributed to it. Transemantics emphasizes test-taking strategies, like knowing it's easier to spot the wrong answer than a right answer. Each class is devoted to a particular drill - vocabulary test, timed analogies, math principles.

Like the others, Stanley Kaplan Educational Center makes no promises about how much a student's score will increase. But Kaplan reports, "Many of our students' [combined] scores go up 200 or 250 points. Sometimes 300 points." Kaplan's program is "teaching them how to think." He says his instructors teach abstract math concepts by using examples from daily life that students can readily understand.

A coaching school probably will bring up your score, especially if you do all the sample tests and homework. But if you've got that kind of motivation, you may want to save your money and buy a book. Buy a Book

The two biggies in the do-it-yourself book market are Barrron's How To Prepare for the College Entrance Examination ($4.95, 653 pages) and Arco's Complete Study Guide for Scoring High - SAT ($5, 411 pages). While neither of the books promises better scores, they are both written on the assumption that study will help. (ETS doesn't go along with this idea. It says that SAT is an "aptitude" test which means it measures knowledge people acquire throughout their lives, not specific skills that can readily be learned.)

Barron's provides much useful information - charts on how to interpret SAT scores, a timetable for test day, and a breakdown of the number of questions that will be asked in each section. The verbal part stresses vocabulary by offering forty word-lists for memorization. The math section is broken into basic study areas such as geometry, quantitative problems, comparisons and interpretation of data. The book also presents a review of such fundamentals as factoring, roots of numbers and equations.

At the back are six sample tests which will take you eighteen hours to complete. Clearly, you can't zip through this self-help book in a few evenings.

Arco's Complete Study Guide is less hefty than Barron's. The introduction reads liek a body-building course - how to build yourself up by improving reading speed and comprehension, developing self-confidence, and "beating those dreaded test-jitters." Pep talk aside, the book offers useful tips. Like Barron's, it emphasizes vocabulary, which it calls "probably the most important element of the test." It offers study techniques: avoid serious study after a heavy meal, do something while studying like taking notes or underlining, don't fiddle around once you sit down to work, and don't be a "skipper" by working only the easy parts of the book.

Arco's discussion of analogies breaks them down into different kinds so you can apply some logic instead of coin-tossing to your answers. "Glove: ball" is an example of a purpose relationship. "Pass: football" is an action: object analogy. The math section is equally detailed with explanations of decimals, percentages, ratios and proportions, distance problems and the computation of interest. Whereas Barron's is largely devoted to practice largely devoted to practice tests and memorizing, the Arco book offers more explanation and reasoning.

ETS is cautious when talking about these do-it-yourself books. "They have some good questions," admits Jim Braswell, "but others mislead students. Some of their analogy and antonym questions are not presented the way we do. And some math parts cover areas the SAT doesn't." But if ETS had its way, your SAT score would be as immutable as your finger prints. Go to the Right School

If you happen to live in Montgomery County (or can afford the $2200 tuition for non-residents), attending Walt Whitman High School might work the right magic on your SAT scores. When it comes to standardized testing, Whitman students outshine the entire country. Last year it had more national Merit semi-finalists - the creme de la creme of high school juniors - than any othe public school. Thirty-one students qualified for this prestige-laden award based on PSAT performances. In addition, according to the latest available scores, average SATs for Whitman students are verbal, 499, and math, 536, both far above average.

Walt Whitman offers no special tutoring sessions or drills for multiple choice tests. It may be reaping the benefits of the SAT's supposed racial and economic bias but there are certainly other factors as well. Notably, the school has more teachers with master's degrees and above - seventy-four per cent - than any other high school in the county. Its strength and secret seems to come from stressing the basics.

All students, for example, spend the first half of the year in their English classes studying such fundamentals as punctuation, capitalization, sentence structure, usage and vocabulary roots. The second half of the year is devoted to "options." Students read such novels as Huckleberry Finn and The Great Gatsby , concentrate on European literature or develop writing skills.In effect, the Walt Whitman English program is very traditional.

And there's no razzle-dazzle in the math department."The teachers hold tight to the curriculum," explains department chairman Robert Miller. "We work straight through a book with homework most every night. We're right to the grindstone."

A student following the usual math progression would study Algebra I, Geometry, Algebra II, Trigonometry, and finally, Advanced Algebra. It may be significant that although students are required to take only two years of math, one of which can be completed in the ninth grade before entering Whitman, eighty per cent of the student body takes a full three years of math.

Miller believes there's a definite correlation between test scores and school progress. "If a student finishes algebra and geometry, he may score in the 400s or low 500s. Algebra II students will be in the upper 500s and the advanced math kids may move into 700s."

Principla Jerome Marco says there are no secret tricks for scoring high on SATs. But like many other people, he easily concedes that a 100 point gain on either math or verbal, "if a student puts his mind to it," is not that unusual. Test Yourself

These sample questions are reprinted with permission of the Educational Testing Service, the copyright holder. Select the lettered pair that best expresses a relationship similar to that expressed in the original pair:

1. CAT: LYNX: (A) crow: eagle (B) cow: ox (C) money: man (D) leopard: panther (E) dog: wolf.

2. SPOILS: VICTOR: (A) scepter: king (B) booty: pirate (C) risk: gambler (D) contest: winner (E) cache: thief.

If you answered number one correctly (E), the Educational Testing Service figures you would score around 380 on the SAT-verbal. Answer number one and two correctly (B) and your score will probably be 490 - a 100 point jump.