If observers were impressed — or dismayed — by the 16.6 percent increase in applications to Yale this year, they ain’t seen nothing yet.

Applications for the class of 2013 will likely surpass this year’s total by a “substantial” amount, Dean of Undergraduate Admissions Jeff Brenzel said. Brenzel, along with high-school guidance counselors across the country, predict that Yale’s new financial-aid policy — which was announced after the Jan. 1 regular decision deadline — may result in an even larger flood of applications next year.

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But toddlers proudly sporting their Eli gear need not discard their stuffed bulldogs just yet.

The number of applications to Yale and the other Ivy League schools — which for the most part has been creeping steadily upward for the past decade or so — could finally plateau in the near future if the numbers of high-school graduates reaches a peak, as demographic data indicates it may.

Next year’s group of high-school seniors — the future class of 2013 — is projected to be the largest graduating class in the history of the United States, according to a December 2007 study by the Department of Education. The number of high-school graduates should decline gradually for the next two decades or so, most likely reaching a trough around 2026, said David Hawkins, public-policy director at the National Association for College Admission Counseling.

Still, there are no guarantees that applications will dip or even stabilize for the next few years.

“I would expect increases for the foreseeable future,” Hawkins prognosticated. “Even though the [high school] population is going to decline slightly, I think we’re in for application increases for at least the next five years.”

By any standards, this year was a record year for applications to the Ivy League.

Yale announced last week that it had received a record 22,528 applications for the class of 2012, while the other Ivy League schools that have released total application numbers so far — Harvard, Princeton and Cornell universities and Dartmouth College — have also reported record totals this year.

Harvard’s announcement that it had received 27,278 applications, a 19-percent increase over last year’s total, may presage a similarly large increase at Yale next year, Brenzel said. He attributed the increase at Harvard in large part to the university’s announcement in December of a major financial-aid initiative for middle- and upper-middle-income families.

Yale followed with a similar aid announcement, but while Harvard announced its new policy before the Jan. 1 regular-decision application deadline, Yale did not.

As a result, Yale will first see the application ripples from its new policy — which dramatically reduces the parental contribution required of families making less than $200,000 a year and eliminates the need for student loans — in the numbers for the class of 2013, Brenzel said.

“Seeing what happened to Harvard’s number, and that our applications went up without the impact of our financial-aid announcement, this definitely has me thinking very carefully about preparing for next year,” Brenzel said.

Although applications at Yale increased by 16.6 percent over last year’s total, the increase from the then-record number of applications two years ago is only 6.8 percent because applications last year were lower than the previous year.

Still, the increase has high-school guidance counselors worried not only about how this year’s students will fare, but also about the possibility of ever-growing piles of applications for admissions officers to wade through.

“I think applications will continue to surge, unfortunately,” said Audrey Reynolds, director of college counseling at Friends Seminary in New York City. “I wish it were different, obviously, because it would give students a better chance of admission.”

Other counselors said they fear admissions officers at Yale and elsewhere would become hard-pressed to devote an adequate amount of time to reading each application carefully if applications continue to increase.

But Brenzel said the admissions office will take the projected increase in applications into account when determining staff levels for next year.

Since the admissions-office staff is still at the same level as two years ago during the prior record application season, Brenzel said, he anticipates that the office will be able to meet this year’s challenge. Having an early admission process also helps, he added, because it spreads out the reading and selection over a longer time period.

Although the Department of Education demographic data suggests that the numbers of students in each high school graduating class will eventually plateau, the constant evolution of the college-admissions landscape may mean that predictions are only valid so long as the major players do not change the rules of the game.

The big rise in applications at Ivy League schools this year, for example, may be a reflection of the decisions of Harvard and Princeton to eliminate their early admissions programs last year.

On the one hand, the students that would otherwise have been accepted early to Harvard and Princeton — and in the case of Princeton, which previously offered a binding early decision program, have been locked into their choices — are now applying to many more schools than they likely would have otherwise.

The changes at Harvard and Princeton have also made many students even more frenzied about the college process than in prior years, high-school guidance counselors said, which has resulted in larger numbers of applications submitted on average per student.

“There is more uncertainty this year among the students because of the policies of Harvard and Princeton,” said Sally Stevens, associate director of college guidance at the private Roxbury Latin School in West Roxbury, Mass. “In order to cover themselves, they need to cast a wider net, which means they need to send out other applications, so presumably a lot of those students are applying to Yale as well.”

The upward spiral in the number of applications submitted by any given high-school senior is a trend that has been in the works for decades, guidance counselors said.

Nationally, there has been “fairly dramatic growth” in the number of college applications submitted, both overall and per student, Hawkins said.

While about 60 percent of students submitted seven or more college applications in 1990, this figure was about 70 percent in 2006, according to the California-based Higher Education Research Institute.

And anecdotal evidence supports these big-picture statistics.

When Reynolds arrived at Friends Seminary 10 years ago, she said, students each submitted six applications on average. Now, that average is eight per student — an increase of 33 percent. And at Phillips Academy in Andover, Mass., the mean number of applications filed by his students went from eight last year to nine this year, Director of College Counseling John Anderson said.

Brenzel said the admissions office is aiming to have a class of about 1300 to 1340 students walk through Phelps Gate next fall. But he said he does not know how many students the office will admit to get to that number, given that Yale’s yield — the percentage of accepted students who choose to matriculate — is hard to predict this year.

“Up until we are ready to release decisions, we will be tracking the matriculation of early admits and trying to decide how conservative we should be with additional offers so that we keep down the risk of overcrowding the College,” Brenzel said in an e-mail.

Like all Yale admits, the 885 students who were accepted early must accept or decline the offer of admission by May 1.

The admissions office will mail notification letters to regular decision applicants on March 31, Brenzel said. The decisions will also be available on the admissions Web site beginning the evening of the 31st.