New high school graduates who think they are finished being judged by colleges and universities should think again. Some are in for a big surprise this summer.

In the admissions offices of schools across the country, officials are poring over second-semester senior transcripts in what University of Pennsylvania admissions dean Lee Stetson calls the "D scholar search" -- the hunt for students who slacked off so much that their grades dropped like a stone, or who dropped tough courses for easy ones.

Thousands will receive a stern letter warning them to shape up for college. Many more will be required to explain the slip in their academic performance. Some could be bounced from an honors program or have their admissions postponed.

And some, who felt secure in their place at a selective college, could be booted for good before they begin. That message -- "We wanted you once, but we don't anymore" -- usually comes in a phone call.

"We do look at the final transcripts," said Shannon Gundy, associate admissions director at the University of Maryland at College Park, where officials are beginning to review the records of every one of the 4,125 freshmen the school expects to enroll.

"Our assumption when we offer admission is that they will have the same level of accomplishment throughout the year. . . . It has been necessary in some cases to take action regarding the application," she said.

Colleges and universities inform students on the application or the acceptance letter that admission is contingent on their performance throughout their senior year, though some seniors admit to glossing over that part, or don't believe it when they do read it.

The warning is an attempt to prevent the situation known as "senior slump" or "senioritis," which involves 12th-graders taking an early break from schoolwork -- and in extreme cases, not showing up for classes. The early decision process, in which students receive acceptance letters before Christmas, could be aggravating the problem, some admissions officers said.

Students said they're not surprised when a college revokes admissions after a teenager gets arrested or suspended from school for such unlawful or prohibited activities as drinking.

But though the counselor and teachers stress that colleges are also watching grades -- history teacher Louise Troutner of Broadneck High School in Annapolis said she has conveyed that message over and over -- many students don't believe it, said Renee Sasso, 18, of Miami, who will attend Alfred University in Upstate New York.

That might explain why students "are really surprised" when they hear from a school during the summer about their second-semester grades, said Robert Croot, admissions dean at Cazenovia College in Cazenovia, N.Y. And some are shocked to find that they will be monitored in their freshman year of college, Emory University admissions dean Dan Walls said.

Each school has its own version of the letters that Texas Christian University admissions dean Raymond A. Brown just sent to about 110 members of the expected freshman class of 1,600. They are missives he calls "FOG," or "Fear of God," letters.

One version goes to about 100 and is relatively mild, asking for a letter "detailing the reasons surrounding your senior year performance." A tougher version, which goes to about 10 students every year, demands an explanation and starkly says: "Please understand that your admission to TCU is in jeopardy."

Of those 10, he said, about half won't respond and will be tossed out, and a few of those who do respond will say, "Gee, I don't know what happened," to which Brown said he replies: "Gee, that's just not good enough." Out they go.

The number of students who see their acceptances revoked might be small, but revocations happen routinely at any school that considers itself selective, counselors and admissions directors said. Often, those who find themselves tossed out are notified so late in the summer that their only option is a community college.

"I don't think it [admissions revocation] is that rare if there is a significant drop," said Mary Lee Hoganson, a counselor at Homewood-Flossmoor High School in the Chicago suburbs. ". . .I do indeed have a file in my office called 'Senioritis,' with letters I've collected over 30 years of college counseling where admission has been revoked. We are talking about maybe one or two students a year."

Schools have standards about what constitutes a "significant" drop in grades. Robert J. Massa, vice president for enrollment and college relations at Dickinson College in Carlisle, Pa., said he recently dealt with "a real tough" case of a National Merit Scholarship winner who failed an Advanced Placement course and received a "D" in two others.

"He just fell off the discipline that won him the National Merit, and we had no choice but to rescind the offer. A real shame," Massa said. When the school gave the student a chance to explain, it learned of a psychological condition that prompted the college to make a deal: The teenager can "redeem himself academically" by attending a community college for the fall semester and achieving at least a 3.0 grade-point average with no grades below B. If he does that, Massa said, he can enter Dickinson in January.

"Typically we won't do that, but because he had some medical issues, we thought it was the right thing to do," Massa said.

Many schools require an accepted student to inform them if the student is receiving a "D" or an "F." Daniel Wright, 18, dutifully did that when he thought he was going to get a "D" in an Advanced Placement biology course at Livingston High School in Livingston, Calif.

Concerned because the University of California had revoked the admission of a friend because of poor grades, Wright said he was relieved when an admissions officer at UC Riverside told him he could still attend the university because only two years of science were required and the biology course was his fourth year. He ultimately received a "C+" in the class.

At the University of Illinois at Urbana-Champaign, the new associate provost for enrollment sent a letter for the first time last spring warning applicants to keep up their grades. Stanley Henderson said he was "absolutely flabbergasted" at the response to his letter from high school faculties, which called him to thank him. He also made a formal request to high schools asking for transcripts earlier than usual.

"If we are going to rescind an admissions offer, we want to do that in a timely enough fashion," he said. "You don't want to do it on the day the student moves into the dorm."

Henderson said that the university has always rescinded some admissions based on grades, but that the rate has been in the single digits. "This year that number is expected to go up," he said.