Strange things are happening in the world of opera. One recent symptom took the form of the Metropolitan Opera's announcement that it was canceling its century-old tradition of touring to other cities.

Then there is the case of the Met's neighbor in Lincoln Center, the New York City Opera, which trembled on the brink of bankruptcy a few years ago. Now, general manager Beverly Sills speaks confidently of plans to liquidate its accumulated deficit.

Meanwhile the Summer Opera Theatre -- a small but artistically impressive operation that uses the Hartke Theatre at Catholic University -- is doubling its season this year. This means two new productions rather than only one, but for a small company it is a significant step. A New Audience

What's happening? All these events relate in one way or another to a single trend. Opera is attracting a new audience, including some who cannot afford most opera tickets and some who have never sat in an opera house.

This audience exists everywhere, not only in the few large cities that boast major opera companies. It became interested in opera at college workshop performances, at the movies, at summer festivals, in church or school auditoriums (sometimes with a piano rather than an orchestra), and above all on the television screen. What has really happened is that opera has come to Marshall McLuhan's "Global Village."

The new audience is unimpressed, sometimes even impatient, with the mystique and conventions of operatic tradition. It likes the established big-name performers but does not need their presence to enjoy itself. It understands that opera was invented long before air conditioning, but in the 1980s it does not see this historic footnote as a reason for limiting operatic performances to the winter season.

It goes to the opera seeking enjoyment rather than social status or a chance to display its furs and jewels. Perhaps for this reason, perhaps because it is used to seeing opera on a screen with subtitles, this audience prefers to know what is going on in an opera, not just to enjoy the pretty tunes. In many cities, it has rallied to the support of small, local companies, and it thinks carefully before paying $50 for a Metropolitan road performance that may fall below local standards.

In companies that are responsive to its demands, this audience is drastically changing the modes of operatic production and presentation. It approaches opera not as a concert in costumes but as a complete theatrical experience, and it has nurtured a generation of young performers who are expert actors as well as singers. It wants a chorus that does not simply stand and sing (as the Metropolitan Opera Chorus often does), but becomes involved in the stage action, the stage picture. It likes productions that look as well as sound good, though it is willing to make allowances for the budget limitations of a small company.

At the New York City Opera, Beverly Sills has used several stratagems to win this audience. One was to run most of her season as a summer festival, when the house normally would be closed. Another was the highly successful innovation of surtitles -- translations flashed on a screen during performances of foreign-language operas. Next fall, the City Opera will try surtitles during English-language performances.

The audience may eventually force changes in the standard operatic repertoire, which has been adapting, in recent years, to pressures that are imperfectly understood. Today, all over the United States, it is possible to hear operas that were composed before Mozart and after Puccini -- operas that were almost unknown a generation ago. The new audience prefers opera in a relatively small auditorium -- more like opera on television. It is buying up all the tickets for The Washington Opera's productions in the Terrace Theater long before those in the Opera House; and all over the country it is supporting the growth of a new kind of opera production -- intimate opera in small houses like the Terrace.

At the Hartke, the Summer Opera Theatre is also venturing into new, speculative areas of repertoire ("Ariadne auf Naxos" and "La Rondine") after years of success with such top-40 works as "La Traviata" and "Tales of Hoffmann." Summer Opera Theatre ticket prices are a small fraction of those charged by the Met. Opera in the Global Village

One reason the Met has canceled its annual tour is that it was losing money. Another is that it can now establish and maintain a national presence without ever crossing the Hudson River.

The company has done so since the 1940s in its Texaco-sponsored radio broadcasts. In the '70s and '80s, this electronic presence escalated dramatically when the Met began a regular series of televised productions. Seeing an opera on television is much more like being there than hearing it on radio. It lacks some of the social dimensions and immediacy of experience that are bought with a theater ticket, but it offers compensations. Close-up shots can bring the audience into the action with an immediacy that is impossible in a large opera house. And subtitles give the experience a dimension of constant, total clarity that is only sporadically available to the average person sitting in a darkened auditorium.

With the arrival of home video, a new freedom has been made available to opera-lovers. For less than the cost of two tickets to the Met, a performance of a favorite opera is available on demand, not subject to the programming whims of PBS or the limitations of the standard opera season. And those who want to play just a favorite scene or aria can go directly to that part of the opera and leave out the rest.

The Met has begun to make some of its televised productions available for home video, including its magnificent "Don Carlo," "Lucia di Lammermoor," "Un Ballo in Maschera" and highlights of its Centennial Gala, on Pioneer LaserDiscs. These are deluxe productions using state-of-the-art video technology, but so far they are available only to a fairly limited clientele. Homes equipped with videotape playback units, Beta or VHS, outnumber those with LaserDisc players by a factor of at least 10 to 1. If it wants to reach the mass audience, eventually the Met will have to release its productions in tape formats.

On the national level, the Met once had a virtual monopoly on first-class opera production. That is true no longer, and the annual tour has been phased out. In the Global Village, that monopoly never existed. The Global Village Opera Company is La Scala, Covent Garden, the Met, Vienna and Salzburg all rolled into one. Every opera production that has been taped for television is potentially available. Once the logistics have been taken care of, the competition should be fierce.

And ultimately, it should improve the quality of opera around the world and the average opera-lover's chances for enjoying this form of art. In the Market

In the last year, two companies have entered the videotape opera field with sharply contrasting products and marketing strategies.

Video Arts International (VAI) has issued some vintage opera movies ("The Medium," "Lucia" and "Der Rosenkavalier") as well as televised opera productions from Europe. It sells by mail order (the address is P.O. Box 153, Ansonia Station, N.Y. 10023), but has made a serious effort to place its productions in record shops and video outlets. It is now being approached by several major video distribution firms and its access to these outlets is expected to escalate in the near future.

Corinth Films (410 E. 62nd St., New York, N.Y. 10021) sells by mail order and concentrates largely on Russian films, including operatic films. Its productions include a 1958 "Eugene Onegin" with the title role acted by one A. Shengelaya but sung by Galina Vishnevskaya (who explains in her memoirs that she was eight months pregnant at the time and did not look much like the virginal heroine). The film is shot on location rather than on a stage, is visually striking and well sung but substantially cut -- by the original producers, not by Corinth.

Also abridged, shot on location and visually splendid is a 1954 "Boris Godunov" (the Rimsky-Korsakov revision), unevenly but on the whole acceptably sung by a cast from the Bolshoi. Both productions have their moments of magnificence, but the prudent shopper might prefer to wait before buying; VAI is currently negotiating for alternate productions of both operas. Those who cannot wait might visit the Opera Loft in the Dupont Circle branch of Olsson's Books & Records, which has copies of these videotapes in an edition imported from Canada.

Meanwhile, VAI has impressively boosted the quality of opera available in Beta and VHS with a brilliant series of tapes from the Glyndebourne Festival in England. There are a few excellent one-shot operatic productions available elsewhere (Zeffirelli's "La Traviata," for example), but this is the first extensive, organized series to be made available on videotape, focusing on the work of a single opera company. And it is magnificent. Besides the Mozart operas ("The Marriage of Figaro," "Don Giovanni" and "The Magic Flute"), which have been Glyndebourne specialties for a half-century, the repertoire covers the entire range of operatic history from the origins to the present. The series extends impressively the variety of opera available on videotape, from Monteverdi's "The Return of Ulysses" to Stravinsky's "The Rake's Progress," both in outstanding performances.

Items in VAI's latest issue are listed below approximately in order of preference, though that is largely a matter of personal taste. All the tapes (Beta hi-fi and VHS) have subtitles, except "The Rake's Progress," which is sung in English. All include the Glyndebourne Chorus and London Philharmonic Orchestra.

Verdi: Falstaff. Donald Gramm, Benjamin Luxon, Elizabeth Gale; John Pritchard conducting (VAI 10). A spirited, superbly coordinated production, particularly treasurable since it contains one of the last performances by that consummate musical and theatrical artist, the late Donald Gramm.

Beethoven: Fidelio. Elisabeth Soederstrom, Anton de Ridder, Robert Allman; Bernard Haitink conducting (VAI-OP-8). The first video production of Beethoven's only opera generates tremendous emotional power.

Stravinsky: The Rake's Progress. Leo Goeke, Samuel Ramey, Felicity Lott, Rosalind Elias; Bernard Haitink conducting (VAI-12). The Washington Opera staged some scenes of this quirky masterpiece with more impact, but Glyndebourne's production is well sung and, on the whole, impressively staged. Affection for it grows with repeated playing.

Monteverdi: The Return of Ulysses. Janet Baker, Benjamin Luxon, Richard Lewis; Raymond Leppard conducting (VAI-11). Musically, this is one of the finest productions this 350-year-old opera has ever had; visually, it gives a good idea of what opera must have looked like in the early baroque era. It may have competition, eventually, from the eccentric but compelling television production directed by Jean-Pierre Ponnelle, but for the moment the VAI issue has a monopoly in the field and it is superb. Both productions would be worth owning for hard-core fans, since they cut the text in different places.

Verdi: Macbeth. Kostas Paskalis, Josephine Barstow, James Morris; John Pritchard conducting (VAI-9). A somewhat uneven production but one that has moments of splendor.