It seems to be getting harder every year to pass the national test required of practicing doctors. According to the National Board of Medical Examiners, 1990 was the fourth year in a row that the failure rate on the basic science part of the national boards, taken by graduates of U.S. medical schools in order to be certified to practice, has hit double digits.

About 16.1 percent flunked the basic science portion of the test, which was administered to 11,816 fledgling doctors last June. The results were the worst showing in at least a decade, although the expected failure rate is around 11 percent.

The unexpected slide in test scores has disturbed both test makers and medical educators. While the questions may have gotten a little tougher over the past 10 years, officials say they do not believe that is the primary reason. Other possible explanations, according to a spokesman for the Association of American Medical Colleges, include the fact that scores on many standardized tests are declining, that students are older and have less science-focused backgrounds and that many students expect to take the exam more than once.

........ 9.1%.. 10.5%.. 8.8%.. 11.8%.. 15.6%.. 13.4%.. 16.1%

YEAR ... 1984 ... '85 .. '86 ... '87 ... '88 ... '89 ... '90

SOURCE: National Board of Medical Examiners, 1990