How much does the public want to know about the public's right to know? Perhaps not as much as journalists wish. But a 90-minute discussion on public TV tonight, dealing with that issue and others, makes an engrossing crash course in shades of gray--legal, journalistic and otherwise.

The program, "National Security and Freedom of the Press," is the first in a series of four taped group-thinks organized under the umbrella title, "The Constitution: That Delicate Balance," by Media and Society Seminars, a project of the Graduate School of Journalism at Columbia University. "National Security" airs at 10 on channels 26 and 32.

Such a flotilla of credentials may make the program sound like a drearily pompous affair. It isn't, though on occasion a few of the 21 participants nudge it that way, and the final third of the program gets into legal matters probably too technical to interest most viewers. It seems a given of current pop thought that it's more important for talk on television to be "lively" than intelligent, but fortunately, much of the talk on tonight's program is both.

Fred W. Friendly, professor emeritus at Columbia and former president of CBS News (the yoke he has to bear in life is that he may be a tad too distinguished), says by way of introduction that the purpose of the seminar, taped last April in Philadelphia's Congress Hall, is "not to change minds on basic principles but to explore the presumptions and stereotypes the media and government may have about each other."

In the exploration that follows, moderator Benno F. Schmidt Jr., a Columbia law professor, posits a hypothetical case of press-government friction: leakage to the media of a Vietnam-like covert action being undertaken by the CIA in "Sierra Madre." Schmidt uses the same techniques of law school colloquy employed by Harvard professor Charles R. Nesson on a recent CBS News broadcast derived from another of these seminars, but unlike Nesson, Schmidt does not come across as a vain ballerina, and God granted him the ability to be succinct.

Retired Supreme Court justice Potter Stewart points out that the Constitution "says nothing about a right to know," and interpreting it as saying something "leads to fuzzy and sloppy thinking." Former CIA director James Schlesinger grumbles that "leaks have become routine and it is virtually impossible to stage a covert operation" anymore anyway, but he doesn't blame the media; he blames "hordes of officials going to the press, handing them documents one after the other."

Dan Rather, anchorman and managing editor of the "CBS Evening News with Dan Rather," says, "As a professional, my job is to publish and be damned." Howard Simons, managing editor of The Washington Post, says of Schlesinger (and thus of all such officials), "I think it's his job . . . to keep secrets . . . My job is to find them."

Brit Hume, the ABC News correspondent, says he would not accept stolen documents offered him by a source but "I'd take a Xerox, frankly" (the fine points get awfully fine as things go along), but the most audacious responses and opinions are those of Lyle Denniston, Supreme Court reporter for the Baltimore Sun, who says, "I don't mind being 'used' at all if I can get a story out of it," finds "breaking and entering" an acceptable way of getting the goods for his readers and notes that his years in Washington have taught him that "lying increases the closer you get to the top."

Other participants include former U.S. attorney general Griffin Bell, Sen. Orrin Hatch (R-Utah), the omnipresent Hodding Carter III and--heard from only briefly in the final minutes of the broadcast--Van Gordon Sauter, the blunt and burly president of CBS News. Scandalously enough, there is not a single woman on the panel. Also, the interpolated commentaries of Friendly and Stewart seem imprudently pedagogic. But otherwise, executive producer Stuart F. Sucherman deserves appropriate commendation for the program, and director Chuck Waggoner enviably manages the no-mean-feat of getting the cameras to the talkers as they talk.

Future programs in this series are "Criminal Justice and a Defendant's Right to a Fair Trial" (Jan. 12), "School Prayer, Gun Control and the Right to Assemble" (Jan. 19), and "Affirmative Action and Reverse Discrimination" (Feb. 2). The project has every external sign of proving to be something of use and value.