Say you're the gatekeeper at an elite university with room for 1,600 new students a year. But 11 or 12 times that many students want in. What kind of hocus-pocus do you use to separate the wheat from the chaff?

At Harvard, whose admissions practices were praised by supreme Court Justice Lewis Powell in his opinion in the Allan Bakke case, the gatekeepers have come up with an intricate six-point system.

The super students - those with grades and test scores that pop your eyes out - get "ones," and are allowed to pass through the gates. Most "twos" also are allowed in. "Threes" are the big maybes. "Fours," "fives," and "sixes" usually receive letters saying, "We're sorry, but . . ."

The numbers are set up by a complicated formula that takes into account test scores, grades, extra curricular activities, character and potential.

But if you happen to be black, Hispanic, Asian-American or an American Indian, you get an extra "plus" added to your number. So if you're a three-plus, with only a dim chance of entering the hallowed halls of Harvard, you're made into a two-minus with a pretty good shot at admittance, according to dean of admissions L. F. Jewett.

You get the same kind of special treatment if you're the son or daughter of an alumnus, happen to live in Cambridge or Boston, or your daddy teaches at Harvard.

Justice Powell might have singled out any of several score universities. But Harvard was singled out, set up as sort of an ideal for the gatekeepers of America.

His ruling put the medical school at the University of california, at Davis, which twice refused to admit Bakke, on the opposite end of the spectrum. That school used a system where it set aside 16 of the 100 spots in each class for members of minority groups.

The prevailing message from the movers and shakers in higher education yesterday was the decision wouldn't change how most schools already do business.

"Only a handful of schools" - perhaps only 10 to 12 - use systems like the one at Davis, said J.W. Peltason, president of the American Council on Education.

Anticipating Bakke-like charges of "reverse discrimination," many medical and law schools have already fuzzed over Dais-like quota systems. "The only problems for the medical schools will be to find the appropriate weight for race among the many factors used in evaluating applicant," said John A.D. Cooper, president of the Association of American Medical Colleges.

The differences between the Davis plan and the Harvard one, it could be argued, are semantic. The results are not dissimilar. The percentage of blacks entering the freshman class at Harvard and Princeton, according to university spokesmen, has varied only a hair during the last five years.

Of the 1,628 freshmen entering Harvard next fall, 8.1 percent of them are blacks, about the same percentage as last fall. Asians are to make up 5.7 percent of the class, Hispanics 4.6 percent - a far larger number than previously - and American Indians, 0.4 percent.

Harvard applicants also are funneled through regional committees, Jewett said. The committees don't have quotas to work with - they aren't, for instance, told to admit 10 students from Montana or 53 from New York City - but they do keep what he called "historical patterns" in mind.

Critics argue the Harvard-style systems sets up informal quotas for race and geography, but doesn't call them quotas. In effect, they say, the gatekeepers are sophisticated enough to pass Supreme Court muster, while the Davis crowd was too crude.

"What [the] Bakke [decision] says is you've got to lie and cheat a little," declares David E. Feller, a UC Davis law professor.

The bitter controversy over university affirmative action programs is an outgrowth of the civil rights movement of the 1960s. Before that time, few blacks applied and even fewer were admitted to prestigious universities. Harvard didn't begin an effort to increase its black enrollment until the late 1960s.

In addition, the whole question of selective admissions programs is largely a post-World War II phenomenon which greatly intensified in the 1960s when the number of college-age youth mushroomed.

Jewett said 1,150 of the 3,100 applicants who applied to Harvard in 1953, the year he entered, were admitted, compared with 1,628 of 12,710 applicants this year.

"It really wasn't that hard to get in back then," he said. "You pretty much admitted most of the people who you thought could do the work in those days."