One by one, the nation’s elite independent universities have joined the Common Application. A student now can apply to the top 20 national universities on the U.S. News rankings with a single application — well, two, if you count MIT.

The one-click application is a fundamental change in college admissions, one that took hold over the past decade as selective independent universities came to view their “signature” applications as roadblocks.

There are still a few exceptions. One is Georgetown University, whose 38-year admissions dean hews to a signature application as a way to frustrate the noncommittal applicant. Another is MIT, a school that presumably will draw the top math-science applicants even if it makes them submit their papers in person.

Some top public universities (including the University of Maryland) have resisted the Common Application, but that’s a comparatively safe choice for a school in a vast public system with a guaranteed pipeline of local students.

But the trend is clear.

Publicly, no admissions dean among the top-tier universities seems to agree with Georgetown admissions Dean Charlie Deacon that the Common Application is stoking a trend of runaway applications. Deacon contends that universities are joining the Common App under competitive pressure, worried about rising applicant numbers at rival schools.

(The actual worrying may be being done by people higher up the university food chain than admissions deans.)

Deacon just returned from a national conference of admissions officials in St. Louis. He said he was somewhat surprised by how many of his peers congratulated him on his stance.

Speaking by e-mail, Deacon said, “Of particular interest to me were the number of those who were deans of admissions who told me they agreed with me but had been pressured to make the move by those higher up in their universities.”

The next top private university to join the Common Application may be USC.

USC ranks 23rd on the U.S. News list — just above UCLA, in case you were wondering — and already collects 36,000 applications every year, more than almost every other private university.

Why bother with the Common App?

The lure of the Common Application is the promise of more apps. Industry wisdom dictates a one-time, permanent jump of 5 to 10 percent in the applicant pool for a college that adopts the Common App, simply because the gesture makes it that much easier for each student to apply.

Mind you, no admission dean I interviewed for today’s Post article cited “more apps” as a significant reason for going Common. The deans — along with their presidents — say they are drawn to the Common App by the promise of a more diverse and democratic applicant pool.

Think of a first-time college attender in a public urban high school. Admission deans picture that kid in the office of her college guidance counselor, completing a Common Application. Admission officials have come to regard the signature application as a vain indulgence for a university trying to reach the broadest possible pool.

It’s also a matter of simple convenience. Why put students through the trouble of typing in their name and address again … and again … and again?

The majority of college counselors and college applicants seem to endorse the Common App.

“The common application is to college admissions what the microwave is to the kitchen,” said Shirley Bloomquist, a college counselor in Great Falls, Va. “It’s fast, it’s convenient and it’s efficient.”

Bev Taylor, a New York counselor who practices under the name Ivy Coach, said, “Students are not happy when they are applying to Georgetown or MIT and they have to go through another application.”

USC was one of the first major universities to use online applications and a largely online processing system in the late 1980s, said Timothy Brunold, dean of admission. USC spent decades refining and simplifying its application and considers its process one of the most efficient in the business.

And yet …

“We get a lot of feedback from the high school counseling community, from the student community itself, telling us that [adopting the Common Application] might be the right thing to do,” Brunold said. “It just makes the process a little bit easier for students.”

Brunold has reservations. “There is a concern that the Common Application leads to more casual applications, applications that are less serious,” he said, voicing a common concern among admission officers.

USC already receives 14 applicants for every spot in the freshman class. He asks, “If we go to the Common App, are we going to be driving the applicant pool so large that we would overwhelm our capability of appropriately reading and considering all of these applicants?”

Charlie Deacon at Georgetown worries about that, too. He’s trying to limit G’town’s applicant pool to about 10 submissions for every freshman seat. Most of Georgetown’s peers have gone well beyond that ratio, and Deacon says he wonders whether those schools really have time to conduct a “holistic” review of each app.

Students who apply to USC tend also to apply to UCLA and Berkeley, institutions that do not accept the Common App. But the same students also apply to Stanford, NYU and Northwestern, all top independent universities that do take the Common App.

Brunold said it is time for USC to make a choice. “We have not decided,” he said, but USC is actively considering the Common Application, perhaps for the freshman class of 2012.

“When you’re out there looking for talent, you want to keep looking for talent, you want to keep looking for fit, in as broad a way as you can,” Brunold said.