About three-quarters of high school seniors are not "proficient" in civics, although most of them do have basic knowledge about democratic government, according to national test results the Education Department released yesterday.

Most of the 22,000 students tested in fourth, eighth and twelfth grades knew the basic structure of government and principles of democracy, but could not apply that knowledge analytically. By the fourth grade, for instance, 93 percent knew that President Clinton is the U.S. president. But among the seniors who took part, 25 percent could not identify two ways the Constitution prevents any president from becoming a dictator.

A similar pattern of basic knowledge but limited understanding has shown up in the results of other national tests in math, science and U.S. history, said Diane Ravitch, a member of the independent board that graded the civics tests. Ravitch described the results of the National Assessment of Educational Progress, a congressionally mandated series of tests, as "very troubling" because half the seniors already were old enough to vote and nearly all will be 18 by the time of the presidential election next year.

"What these young voters know and don't know about civics and government will have an impact on all of us through the way they carry out this most crucial responsibility of citizenship in a democracy," said Ravitch, a former assistant secretary of education.

The seniors' limited understanding of civics was mirrored in other grades as well. At each grade level, about three-fourths of the students tested did not demonstrate the proficiency that a board of educators, officeholders and business leaders judged they should have.

Charles N. Quigley, executive director of the Center for Civic Education, said other recent studies of how much American youngsters know about politics and government have had a similar outcome.

"One of the major reasons students did not do well . . . is that the vast majority either are not being taught civics and government at all or they are being taught too little, too late and inadequately," Quigley said. He blamed states and school districts for not requiring enough instruction in the subject, which he said was necessary to a fundamental purpose of education: learning how to become responsible citizens.

Education Secretary Richard W. Riley suggested that adults who do not vote and have grown cynical about politics also bear some responsibility for the test results. "If adult Americans will not model civic responsibility, how can we expect our young people to be any different?" he asked.