Humanities programs at U.S. colleges have declined so sharply over the past two decades that most students graduate "lacking even the most rudimentary knowledge about the . . . foundations of their nation and their civilization," William J. Bennett, chairman of the National Endowment for the Humanities, said yesterday.

Bennett charged in a 42-page report that the traditional liberal arts curriculums, which splintered under the assaults of student activists in the 1960s, remain "dissolved" because of the pressures of specialization and marketing.

To reverse the decline, he said, students at all colleges should be required to take a "core of common studies" about western civilization, taught by each institution's top faculty members.

"Most of our college graduates remain shortchanged in the humanities," said Bennett, who has taught law and philosophy at several universities. "The fault lies principally with those of us whose business it is to educate these students."

Bennett has been mentioned as a leading contender to replace Education Secretary T.H. Bell, but he said in an interview that there is "no connection" between his new report and the possible appointment and that "it would break my heart if it were read that way."

Bennett said the report, called "To Reclaim a Legacy," is based on discussions and papers prepared by a 31-member study group on higher education that he convened in March and on data from several higher education surveys.

Bennett's report, the first to deal solely with the humanities, said that, on many campuses, humanities "have been siphoned off, diluted, or so adulterated that students graduate knowing little of their heritage."

According to the report:

*From 1970 to 1982, the number of college students graduating with bachelor's degrees in English dropped by 57 percent; in philosophy, by 41 percent; in history, by 62 percent, and in modern languages, by 50 percent. At the same time the total number of degrees awarded rose by 11 percent.

*Forty-seven percent of all U.S. colleges require foreign language study for the bachelor's degree -- down from 89 percent in 1966 and 53 percent in 1975.

*A student can get a bachelor's degree from 72 percent of all U.S. colleges and universities without having studied American history or literature; from 75 percent without studying European history; and from 86 percent without studying about classical Greece or Rome.

"The sole acquaintance with the humanities for many undergraduates comes during their first two years of college," Bennett said, "often in ways that discourage further study."

Bennett said every college should develop required humanities courses, spread throughout the undergraduate years and probably accounting for about one-quarter of all courses that a student takes. He said the writings should range from Homer, Shakespeare and the Bible to Marx, the U.S. Constitution and Martin Luther King Jr.

"We are a diverse culture but we have a common culture, too," Bennett said. "There are things that we share as a people."

Although students should be required to attain "some familiarity" with at least one major nonwestern culture, Bennett said, the humanities core should concentrate on western civilization.

The report describes three "bright spots" -- Brooklyn College in New York, St. Joseph's College in Indiana and Kirkwood Community College in Iowa -- where the "drift toward curricular disintegration has been reversed." But it says most colleges "have lost a clear sense of . . . purpose" and have allowed "the thickness of their catalogues to substitute for vision and a philosophy of education."

Study panel members included Hanna H. Gray, president of the University of Chicago; John R. Silber, president of Boston University; Donald M. Stewart, president of Spelman College; Harvard University sociologist David Riesman; and Mark H. Curtis, president of the Association of American Colleges.