Hallelujah! (Somewhat.) Wolf Trap Farm Park, after having been given the shaft by the Metropolitan Opera Company for several seasons, has swung a heavy enough stick that this summer's operas will be the strongest in repertoire and in casting yet to come this way.

Most important, James Levine, the Met's music director, will conduct three of the six operas to be given here on June 49. They will include Verdi's "Otello" on June 6, "Don Carlo" June 8, and this season's revival of Smetana's "Bartered Bride" June 9. James Conlon, who has been conducting "Tosca" this season in the big house, will be in charge of it here, when the Met's week opens on June 4. And Nicola Rescigno, whose conducting of opera in Washington goes back nearly 30 years, will be at Wolf Trap for Donizetti's "Don Pasquale," on June 5.

One of the major excitements of the week will come on June 7 when Richard Woitach conducts Poulenc's "Dialogues of the Carmelites," in the first performance of this great, recent opera in the Washington area. Woitach will be replacing Michel Plasson, who conducted the "Carmelites" at the Met two years ago when it was first given there. At that time, he led the score with distinction, shaping its sensuous phrases with notable plasticity. This season, however, the performance heard over the Texaco broadcast was strangely square and lacking in feeling much of the time. Perhaps Woitach will find the key to the kind of moving experience the opera can provide.

The week's repertoire offers Wolf Trap audiences two of Verdi's great works in "Otello" and "Don Carlo." While "Otello" has been heard here with some frequency, most recently from the Paris Opera, "Don Carlo" is strangely missing from the active repertoiro of most companies. To its great credi, the Met is giving the work in the most complete version it has yet presented, though that is not as earthshaking an announcement as it might be had "Don Carlo" entered the Metropolitan repertoire earlier than the Rudolf Bing era it ushered in less than 30 years ago.

It stands, however, as one of the greater monuments in the Verdi lists. The cast to be heard here is not the Met's first cast of principals, lacking Renata Scotto, Marilyn Horne, Sherrill Milnes and Nicolai Ghiaurov. In their places, Gilda Cruz-Romo, Nadine Denize, Ryan Edwards and Jerome Hines will be heard. "Don Carlo" is the only opera in which such major cast changes are being made. The "Tosca" cast will be headed by Leonie Rysanek, who sang up an exciting storm in the role when she was here with the Deutsche Opera several years back. She will be joined by Vasile Moldoveanu as Cavaradossi and Cornell MacNeil as Scarpia.

The title role of "Otello" will be sung by one of the greatest exponents of the part to be heard anywhere today, Jon Vickers. His towering portrayal stands as one of the finest performances on any opera stage of our time. Again, as in the "Don Carlo," Scotto will be replaced by Cruz-Romo, who should find the role of Desdemona highly congenial.

The only alteration in the cast of "Don Pasquale" from the regular New York cast will be the appearance of Roberta Peters as Norina in place of Beverly Sills. To any who have seen and heard Sills in the part this season, her acting and her singing both will be missed, for she has made the part one of her finest. Peters is, however, a seasoned artist who knows the role inside and out. And she will be partnered by Nicolai Gedda's Ernesto, Fernando Corena in the title role, and the superb Swedish baritone, Hakan Hagegard, as Doctor Malatesta. Hagegard became a star to all who saw Ingmar Bergman's film production of Mozart's "Magic Flute," in which he turned in an inimitable Papageno.

In "The Dialogues of the Carmelites," the late Francis Poulenc wrote one of the most beautiful operas of this or any century. The true story is based on the death on the guillotine of a community of Carmelite nuns during the French Revolution. The Metropolitan presents the work in English, which, while it removes the exquisite sound of the original French text, puts its highly credible story clearly before the audience. The production, by John Dexter, is one of the handsomest and most dramatically effective in Met history, doing full justice to the work.

The cast, most of whom have been together in the work since its first Met hearings, includes Regine Crespin as the Old Prioress, in a tremendous role. In 1957 when the opera was new in Paris, Crespin sang the New Prioress, a role being sung here by Clarice Carson, who replaces Leona Mitchell from this season's cast in New York. Maria Ewing is the Blanche, and Mignon Dunn sings Mere Marie.

A wise decision was made by Wolf Trap and the Met for this summer's week of opera, in omitting a Saturday matinee. Experience has proven that the brilliant early June sun and the probability of either extreme heat or cold or rain, all of which have plagued recent Met weeks in the park, are at their most undesirable in mid-afternoon.

The cast for the revival of "The Bartered Bride," -- which is better translated as "The Sold Bride," but at this point who is going to make the shift? -- is a strong one. Patricia Craig will sing in place of Teresa Stratas, who sounded strangely uncomfortable as Marenka over the air. And while Martti Talvela is probably without peer today as Kecal, the marriage broker, Ara Berberian is an outstanding comic bass who should handle the part strongly. In what is unusually luxuriant casting, two leading tenors, Jon Vickers and Nicolai Gedda, are heard as Vasek and Jenik. Smetana's is one of the finest comedy operas, and if played with the right feeling, has no precise parallel.

In the face of this much good news, Wolf Trap's Metropolitan week should set a high standard.

Nor is the remainder of the summer without its highlights for lovers of orchestral music, ballet, more opera, and, in something of a new venture, more solo recitals and chamber music, the latter from the newly formed Concert Soloists of Wolf Trap, under the artistic direction of Earl Wild. With guitar, flute, harp, violin, cello and piano, these can offer a wide variety of styles and combinations.

The summer's orchestras will include the National and the Philadelphia, under conductors Rostropovich, Ormandy, Copland, Conlon, Slatkin, Nelson, Rudel, Caldwell, Badea and Irving. There will be opera nights, including the Wolf Trap Company in Vittorio Giannini's "Taming of the Shrew," with Anna Moffo in the Katharine role. Other soloists include Leontyne Price with the National Symphony, Barry Tuckwell, horn, Andre Watts, piano, and the University of Maryland Chorus, joining the National Symphony in Haydn's "Creation."

Dark clouds are gathering over Wolf Trap at present, with the greatest threat to its future as a home of fine music now moving through the Virginia legislature. If four more lanes of unrestricted automobile traffic are added, two each on either side of the present Dulles Access Road, it is hard to see how Wolf Trap can long continue to offer operas and concerts.Even now the noise from the road and airplanes drowns out the music a number of times during every program. Those with long memories will remember how operas and concerts at the Watergate (pre-Nixon) were eventually ruined by the same two factors. But with the coming of Tyson II, the building of a World Trade Center two miles east of Dulles, and the steady growth of the metropolitan area right through Wolf Trap country, it is hard not to think that the Park's days of beautiful music are numbered. So enjoy it while you can.