THERE SEEM TO BE times in modern societies (probably when no wars are being fought or frontiers conquered) when people start feeling guilty about having too much leisure time, and resolve to put it to better use. They take well-planned weekend trips to places of maximal educational value and listen to cassettes of the Britannica while driving to the supermarket. They start jogging, which leads to marathons, which spawn triathlons (a mixture of too much running, bicycling and swimming).

But the most reliable indicator of whether we are in one of these periods of earnest endeavor is -- as it has been for the past century -- the number of people willing to stand packed together listening to the entire "Ring" cycle of operas by Richard Wagner.

This month the San Francisco Opera has been putting on the "Ring" for one standing-room-only audience after another. When the company announced last fall its intention to stage the four operas that make up the cycle, it was hoping for nothing more than a full house and some recognition. It got the recognition along with an avalanche of requests for tickets -- enough to fill many houses. Two additional performances of the cycle were scheduled. Closed-circuit telecasts were made to an adjoining auditorium for the many who couldn't get in. And at each performance polite crowds stood in line for hours for standing-room tickets.

The Ring is a complicated story of Nordic gods, heroes, dwarfs, dragons and flying horsewomen, of incest, treachery, greed and male chauvinism. Although not to everyone's taste, it is an overawing spectacle, but one that even most devotees are content to take in "Gone With the Wind"-size chunks of four or five hours, and at irregular intervals. To sit, let alone stand, through the four installments in fairly rapid succession, for a total of 16 hours, is a certifiable achievement.

It isn't the end, however. A film biography of Wagner running 91/2 hours was sold out in limited engagements this month here and in New York. The film (which stars the late Richard Burton) had previously been shown in Europe as a TV miniseries, but a miniseries is only a diversion, while a 91/2-hour megamovie is an experience -- perhaps the ultimate one for exhausted Wagnerians in San Francisco, where it is to be shown Saturday night. The movie is described by critics as rather static and not too musical.

The current wave of earnest endeavor has probably crested. We expect it will dissipate itself with a series of three-day-long Proust readings in public parks, the showing of a 10-hour movie on monetary policy in major cities, and a spate of newspaper stories on how people are spending their weekends taking really comprehensive tours of museums of natural history, with no skipping over the exhibits of rocks and insects. Soon afterward, if history is any guide, this sort of productive activity will wane, and there will be a resurgence of goofing off.