Ohio Wesleyan University has its smallest freshman class since World War II. Only 448 new students showed up this fall, down from 662 a year ago, a drop of 32 percent.

A major psychological and economic blow to the well-regarded, 140-year-old liberal arts college, it is symptomatic of a disturbing trend that threatens many institutions across the country.

Freshmen enrollment was down at two-thirds of the nation's 1,500 private colleges and universities this fall, according to a new study by the National Institute of Independent Colleges and Universities. One-third experienced a drop of 10 percent, and 15 percent suffered a drop of 20 percent or more.

Small, midwestern liberal arts colleges, like Ohio Wesleyan, were hit hardest by the declines, but the fallout of the trend was felt even at the nation's most selective colleges and universities.

Overall, freshman enrollment fell by 17,000 students, a drop of 4.1 percent. The study estimates that colleges thus will lose $250 million in tuition during the next four years.

The enrollment declines were the first since the end of college deferments during the Vietnam war. Not surprisingly, they set off soul-searching and belt tightening at places such as Ohio Wesleyan, a Methodist-affiliated college located in this town of 19,000 about 25 miles north of Columbus.

"I'm of the belief that the number of small colleges like this will be drastically reduced," says Verne E. Edwards, a journalism professor. "Some, like Ohio Wesleyan, will survive, but the weeding out will be traumatic."

Experts blame the decline in freshmen on several factors:

* The sluggish economy.

* The end of the baby boom, meaning fewer college-age people than a few years ago. The Census Bureau projects there are 4.19 million 18-year-olds in the nation, compared with 4.3 million in 1979. By 1990, the number will drop to 3.4 million.

* Reagan administration cuts in student aid and threats of future cuts. The number of federally guaranteed student loans dropped by 780,000, or 22 percent, last year after the administration tightened eligibility requirements, according to the Education Department. Widespread confusion over the cuts caused many students eligible for such loans not to apply.

* An increased interest in technical and professional educations instead of liberal arts. Of the nation's 12.4 million students, 4.7 million now attend two-year community colleges and technical schools.

* A growing tendency of students to go to public universities and community colleges, both of which recorded enrollment gains this year. Ten years ago 76.6 of all college students attended public colleges; today that is up to 78 percent.

Cost is the key. This year tuition and room and board come to $8,870 at Ohio Wesleyan, compared with $4,310 at nearby Ohio State.

Ohio Wesleyan, which draws about two-thirds of its student body from the economically depressed East, had two additional problems this year. It received some bad publicity and embarked on a program to make the college more selective.

Concerned about a gradual "slippage" in standards, the college started a "Reach for Quality" program in 1981 that projected reducing enrollment to 1,800 by the fall of 1985. Enrollment had peaked in 1970 at 2,500.

Eastern prep schools were quietly told that Ohio Wesleyan would no longer serve as "a dumping ground" for problem students who couldn't get into Ivy League colleges. A similar message about "less than qualified students" went out to public high schools.

The plan worked -- too well. The college claims its best freshman class in five years: Scholastic Aptitude Test scores climbed by 12 points, and the number of freshmen from the top one-fifth of their high school class climbed 5 percent.

But the college, which had planned for a smaller freshman class, got one far smaller than it had bargained for: 448 instead of just under 600. "We took some calculated risks in being more selective," says Thomas E. Wenzlau, president of the college the past 13 years. "Quality turned out to be more expensive than we thought."

The bad press came in the form of an unflattering portrait of the college in the "Selective Guide to Colleges," written by Edward B. Fiske, a New York Times reporter.

"The administration at Ohio Wesleyan says that it is looking for students interested in a wide range of nonacademic options," Fiske wrote, "but it seems to have collected a student body interested mainly in a good time."

Faculty and students here almost unanimously disagree with that characterization. Although half the students belong to a fraternity or sorority, they insist campus life is no wilder here than at other places.

But Fred E. Weed, dean of admissions, says the damage has been done. He and others here estimate the Fiske report cost the college as many as 100 freshmen.

"The Fiske report hurt us. I talked to the parents of three students who withdrew after reading it," Weed says. "They didn't like what they read, and no amount of talking would change their mind."

Weed is leading a recruiting drive for next year, and efforts are under way to recast the college's image.

Meanwhile, Ohio Wesleyan, built on the site of an 18th-century health resort, has decided to cut its 178-member faculty by 25 in the next three years, eliminate two departments and consolidate several others, drop some physical education requirements and trim maintenance costs.

But Wenzlau and faculty members interviewed are surprisingly optimistic. Wenzlau says the dramatic enrollment drop may actually prove to be a blessing because it has forced the college to deal with problems that will be common in the 1980s.

"Virtually every institution is going to be faced with cutting down its size," he says. "There will be some that won't survive. Ohio Wesleyan will make it because we're prepared."