Medical students at Harvard University have improved substantially over the last six years in their performance on a national licensing examination given doctors in the final year of medical school.

In 1974, seven percent of Howard graduates failed the exam -- 3 1/2 times the national failure rate. Now, 99.5 percent pass, compared with the national average of 98 percent.

Howard's College of Medicine, where 108 new graduates took the Hippocratic oath last Saturday, improved its students' standing by making the test a requirement for graduation, according to the dean, Dr. Russell L. Miller.

"I don't think we're seeing a new generation of students and I don't think we're doing things a whole lot differently," Miller said. But "when an individual . . . . finds he has to perform at the level of his ability -- you usually dip into your resources and do what has to be done."

He said that in recent years the caliber of students at the predominantly black school has improved steadily. The faculty members have also stressed the importance of the national examination, designing their own tests to include similar kinds of questions.

The examination is Part Two of a three-part test administered by the National Board of Medical Examiners. Given a few months before graduation, it tests knowledge of diseases and diagnosis. Medical students take Part One -- which tests factual knowledge of anatomy, biochemistry and other sciences -- after the first two years of medical school, and Part Three -- which measures ability to interpret laboratory tests and make treatment decisions -- after the first year of residency.

Despite Howard students' improved performance, Miller said he worries that in the next few years the economy, decreasing political pressure for affirmative action and a national shift away from higher education will combine to lower the number of black students applying to medical schools.

Miller said that, although black applicants to medical school are better prepared, they are not applying in increasing numbers, and the proportion of blacks in the nation's medical schools has begun to decline.

The number of places available is American medical schools rose 45 percent in the 1970s, as new schools opened and existing ones expanded. Until the mid-1970s, with the help of affirmative action programs, more and more blacks entered medical school. In 1974, according to the Association of American Medical colleges, 1,106 black students were enrolled in the first year of training.

But in 1979, despite the schools' continued expansion, the number of black students in their first year was almost identical, 1,108. Only 5.8 percent of American medical students were black.

Miller said several factors are responsible for the arrested progress: College and medical school admission committees are less aggressive about affirmative action than they were five years ago. Economic pressures and changes in the nation's attitude toward higher education are making it harder for blacks to go to college and graduate school. Those who do may be diverted from medicine by increasing opportunities for minorities in business and other fields.

And, with a surplus of doctors predicted by the mid-1980s, the government is moving to phase out aid to medical education and to cut federal loan money available to medical students.

Miller said medical schools still compete to recruit the most qualified black applicants, but that Howard has fared well because it attracts students who agree with its priorities -- to train practitioners, not researchers and specialists.

He said a survey of Howard graduates a few years ago showed 75 percent returned to their home towns or geographically similar communities to practice, and 90 percent function as the primary doctor for their patients, rather than as consultants.

Since 1977, Howard students have been required to pass Part One of the National Board exam at the end of their second and Part Two at the end of their fourth year.

Miller said about 23 percent of the students fail Part One the first time they take it, compared with a national failure rate of 12 percent.

Those who fail are required to repeat the test three months later, after a summer of intensive study. After two tries, about 97 percent of the class passes, he said.

The handful of students who fail Part One a second time are not allowed to proceed to hospital work. Instead, they enter a special year of courses designed to emphasize areas in which their medical knowledge is weak. If they improve, they take the test a third time the next spring.