As colleges weigh this year’s round of applications, high school seniors are not the only anxious ones.

Just as nervously, colleges — facing a financial landscape they have never seen before — are trying to figure out how many students to accept, and how many students will accept them.

Typically, they rely on statistical models to predict which students will take them up on their offers to attend. But this year, with the economy turning parents and students into bargain hunters, demographics changing and unexpected jolts in the price of gas and the number of applications, they have little faith on those models.

“Trying to hit those numbers is like trying to hit a hot tub when you’re skydiving from 30,000 feet,” said Jennifer Delahunty, dean of admissions and financial aid at Kenyon College in Ohio. “I’m going to go to church every day in April.”

In response, colleges are trying new methods to gauge which applicants are serious about attending: Wake Forest, in North Carolina, is using Webcam interviews, while other colleges say they are scrutinizing essays more closely. And they are making more vigorous appeals to try to convince parents and students who will be offered admission in April that theirs is the campus to choose. But mostly, they are guessing: Will pinched finances keep students closer to home? Will those who applied in December be feeling too poor to accept in May — or show up in August?

Colleges have been in the catbird seat for the past decade or so. As the number of high school students swelled, applications rose, allowing colleges to be more selective. And families benefiting from a flush stock market seemed willing to pay whatever tuition colleges charged.

But all that has changed. For students, the uncertainty could be good news: colleges will admit more students, offer more generous financial aid,and, in some cases, send acceptance letters a few weeks earlier. Then again, it could prolong the agony: some institutions say they will rely more on their waiting lists. But there is no question, admissions officers say, that this year is more of a students’ market.

“It’s like the dot-com bubble burst for higher ed,” said Barbara Fritze, vice president of enrollment at Gettysburg College in Pennsylvania. “We’ve been in this growth mode for a period of time. Now there’s a real leveling going on.”

Colleges consider an amalgam of factors, comparing them to past trends, to predict whether a student will attend, including, for example, what high school he went to; the strength of his grades, scores and recommendations; how much financial aid he has been offered; and whether he plays the cello or wants to study ethnobotany or economics. (If he is a she, the equation looks different still.)

They consider how many phone calls, Web hits, campus visits and applications they have received. They look at how many students put down a deposit in May, then assume a bit of “summer melt.”

If it sounds complicated, it also works. Kenyon, for example, has hit the magic hot tub each of the last five years.

But with high gasoline prices last summer, many campuses reported fewer visits, throwing off one of the better indicators of which applicants are serious.

Applications, too, have been unpredictable. Some public institutions have seen increases of 30 percent. But with almost every state cutting budgets, it is unclear how many applicants those institutions will accept — California and Arizona, for example, are capping enrollment. And private colleges are waiting to see how much public institutions raise tuition; most do not set rates until state budgets are firm.

Meanwhile, applications are down at many private institutions. Colleges and high school guidance counselors say more students are applying to so-called financial safety schools, where they are confident of getting scholarships, even if it means attending a less selective institution.

Officials say parents are reluctant to commit to four years of an expensive private school, worried that their companies might be restructuring. At Kenyon, one mother, after e-mailing to say that the family could not afford the college’s early decision offer, e-mailed two hours later to say they were reconsidering, then e-mailed again two hours after that to say that her son would attend, after all.

“It’s a consumer confidence issue,” said Steven Syverson, vice president for enrollment at Lawrence University in Wisconsin. “Families are feeling like they can’t afford it even if they’re in the same financial position they were three months ago.”

The Internet has thrown off another marker: applicants used to have to call or write for a catalog, giving the college an early signal of their interest. Now, many campuses say 25 percent to 30 percent are “stealth applicants” — the first the college hears of them is when they apply.

Some enrollment officials theorize that applications are down because cost-conscious applicants have made their choices more carefully. Then there is the glass-is-half-empty view, more common at private institutions where applications are up: students set their hearts on where to apply last summer, before the big crash, but will be choosing less expensive schools this spring, as economic indicators plummet.

Institutions had been trying to cut back on the number of students they accept early, believing they would end up with a more economically diverse freshman class; those who are admitted early forfeit the right to shop around for financial aid offers, so are frequently wealthier. But this year, many said they had accepted more early decision applicants, trying to lock in as many students as they could in December.

Still, that may not be a guarantee. Colleges say more and more early decision applicants are circling back to bargain for better financial aid packages, or asking to be released from their agreements so they can consider more generous offers.

So as public institutions say they will accept fewer students, many private schools say they will accept more. The 13 members of the Associated Colleges of the Midwest, which includes Carleton, Macalester, Grinnell and Colorado Colleges, plan to accept 10 percent or 11 percent more applicants, said the group’s president, Christopher Welna, to make up for about a 10 percent decline in applications. Hamilton and Gettysburg, among other campuses, also plan to accept a slightly bigger proportion of applicants. And Marquette University, in Milwaukee, said it would accept up to 600 more applicants to its class of 1,900, even though applications are up 17 percent.

Campuses, meanwhile, are trying to determine — and encourage — applicants’ intentions. Kenyon will write to the parents of accepted students, to reassure them that financial aid will not dry up over the coming years.

And at Gettysburg, Ms. Fritze plans to send out acceptance offers a bit earlier, hoping to generate loyalty.

Barmak Nassirian, the associate executive director of the American Association of Collegiate Registrars and Admissions Officers, says the first real indication of who is coming could be in May, when students put down their deposits.

“But even that,” Mr. Nassirian said, “may be an overestimation.”