As many as 163 Montgomery County high school seniors are expected to gather today at Walt Whitman High School to sweat out another round with the dreaded college entrance exams because the test they took in December vanished mysteriously.

"Everyone is really upset," griped 17-year-old Dahane Corn, one of more than 100 Walt Whitman seniors among the students whose test scores have apparently been swallowed between here and Princeton, N.J., where Educational Testing Service scores the exams. "Nobody wants to sit through three hours of hell again," she said.

Without the results of this threehour ordeal, many college-bound high school seniors have missed application deadlines and have had their higher education plans thrown into confusion at a time when anxiety runs high.

"It's hurt me," said Whitman student government association president Hank Kline, who was hoping to get an early decision from Duke University. "Duke won't see a new set of scores before they decide."

"The scores are apparently lost in the mails," said John Smith of Educational Testing Service which prepares and scores Scholastic Aptitude Tests (SAT) for more than 1.2 million students each year. "I can't deny that they weren't received, but they just haven't been found."

Whitman has a reputation for producing bright students who polish off the SATs in their junior year, but most of the 375 students taking the exam Dec. 1, according to guidance counselor Edward Shuma, were seniors trying to better earlier scores. A few of the test-takers were also from John F. Kennedy High School.

Shuma wrapped two packages together with strapping tape and put the bundle in the mail the Monday after the tests were taken. With the SAT answer sheets were achievement test answers. What Puzzles him is that the achievement tests were received, scored and sent out.

"The Educational Testing Service implied it never received the papers," Shuma said. "It infuriated me no end. I got a lot of phone calls."

The testing service finally notified students last week that their scores had never been received.

"We were waiting and hoping they would show up," said Smith. "The students will be retested at our expense and the test will be hand-scored as soon as possible."

In the last six weeks of nail-biting, many students have not only missed college application deadlines, they have lost the mental sharpness built up through preparatory courses and hours of study in the weeks leading up to the tests.

"I studied a lot and got totally psyched up," said Corn, who is applying to Amherst, Yale, Brown and other colleges. "The first time I took the test I didn't feel too good. This time there was a lot less I didn't know. The idea of going through that big treacherous test again for ETS's mistake is what kills me."

Trying to get into Williams or Middlebury College, 17-year-old senior Bill Hildreth memorized 963 vocabulary words including 'chimerical,' 'lugubrious' and 'termagant.'

"A termagant is a noisy boisterous woman," he said. "What irritates me is that by December I was prepared. Now I can't remember some of the words further down on the list."

"You don't know what a pain those tests are," said Julie Evans who missed the Jan. 1 deadline for getting new SAT scores to Bucknell and Trinity colleges. "Applying to schools is a time-consuming process. This is just one more roadblock."

The testing service says it will attach a letter of explanation when it mails out test scores to the various colleges to which Whitman students have applied.

"This doesn't happen very often," Smith said.