After 10 months as education secretary, William J. Bennett broke a near silence on one of the most persistent and hotly debated problems in American education -- the tens of millions of adults who are functionally illiterate.

In a Senate hearing on literacy yesterday, Bennett laid out what he called his "guiding principles" for federal involvement in combatting adult illiteracy. These include an emphasis on prevention -- by stressing reading early in elementary schools -- while leaving to state capitals and the business world the primary responsibility for initiating literacy training programs.

Adult illiteracy entered this year's national educational debate with the publication of "Illiterate America" by Boston author Jonathan Kozol. In a nationwide book promotion tour, Kozol demanded an infusion of federal funds to combat illiteracy, provoking fresh concern about the issue on Capitol Hill.

When Bennett and Kozol appeared opposite each other on ABC News' "Nightline" in the spring, the education secretary sometimes appeared flustered and frustrated in commenting on a topic about which some aides said he felt uncomfortable. Since then, Bennett has spoken on topics ranging from religion in schools to the classics, but has avoided discussing illiteracy.

Now Bennett has planned a series of events centering on that issue. He met Tuesday with literacy advocate Barbara Bush, wife of Vice President Bush, and today he plans to meet with Rep. William F. Goodling (R-Pa.), sponsor of a key House bill aimed at fighting illiteracy. Next Tuesday, Bennett will attend a news conference unveiling a new "War on Illiteracy" being launched by ABC and PBS, the public broadcasting network.

Yesterday's task force hearing on literacy was chaired by Sen. Steve Symms (R-Idaho) as part of the Senate Republican Conference.

Bennett offered no new initiatives but said his department would begin better coordination of existing programs. "We want to work with other departments in efforts to address illiteracy," Bennett said, "in employment, in health care, in our system of justice. We must work even more closely with the Department of Labor through various job-training programs."

Bennett took issue with the various figures used to quantify illiteracy in the United States. Kozol, in his book, says one-third of all adult Americans -- about 60 million -- are functionally illiterate, and an August report by the Northeast Midwest Institute, a think tank, said 60 million adults cannot read the front page of a newspaper.

Bennett said yesterday that the actual number was between 17 million and 21 million, based on results of a 1982 Census Bureau test of English language proficiency.