THE Washington Opera has ended its 10-week season, the company's first extended repertory season, in a state of real distinction.

One hesitates to use so strong a word as "triumph" only because the glitter and pyrotechnics implied by the word are misleading. Lavishness isn't what the Washington Opera is shooting for.

What happened here this year is an achievement that holds much more promise for the future. The company has thrown out the old approach -- based on mostly borrowed productions and hit-or-more-often-miss programming -- that marked most of its first 25 seasons. Five of this year's seven productions were new and six were the company's own. Also, the old scatter-shot scheduling, between cracks in the Kennedy Center Opera House's season, was abandoned. Washington had a real opera season of its own, shorter than in San Francisco or New York, but with a sense of a sustained event. For performers -- and this does not mean just singers -- it meant a greater chance to concentrate and polish their work.

The upshot was that the season added up to more than the sum of its parts. The new methods gave significantly greater control to the three persons who contributed most to the turnaround -- general director Martin Feinstein, conductor and former music director John Mauceri and designer Zack Brown.

It was a performance late in the season -- one that I expected to be routine -- that convinced me that the new level of qualify rested on firm foundations and that the preceding series of successes was not merely a sequence of happy flukes. It was the only revival from the previous year, a small-scale version of Rossini's "The Barber of Seville" in the Terrace Theater. I had disliked it before. The small orchestra required in that pit seemed too thin for Rossini's delicate and witty orchestration, even under the splendid Mauceri. The solo playing was so rough that many segments were disfigured. The comedy seemed too broad for a theater of 500. And except for J. Patrick Raftery's deservedly acclaimed debut as Figaro (repeated this year) much of the singing was short on style.

Further, that event reinforced doubts about some of the uses of the Terrace. The opera's management asserted the Terrace was better -- and cheaper -- for certain intimate operas. One wondered, after seeing "The Barber of Seville" if it wasn't being used instead for some shoestring versions of works that belonged in the big house, but that the company couldn't afford there.

But by near the end of this year's run, after rigorous rehearsals, 10 performances, a few cast changes and management's insistence on stronger players for the Terrace Theater orchestra, "Barber" was transformed. You could tell right off. In the overture, the players were giving Mauceri the kind of grace and wit they lacked before. It wasn't the last word in polish, but that really wasn't necessary.

The singing and acting were even better. Raftery's Figaro was just as spirited and wellsung. But, far more important, the other characters had learned to relate to each other in a credibly comic way. And there was a flowing sense of musical ensemble that often eludes even the greatest singers in the "Barber" unless they have been carefully prepared. Janice Hall's Rosina was especially charming; she had an unaffected vocal and acting style that freed her of the unctuous girlishness most Rosinas feel they have to pour on to be convincing.

As for the Terrace possibilities: It was in the Terrace that the company presented its boldest and most illuminating production, "The Rake's Progress," that astringent and absorbing marriage of Stravinsky's music with a text by W. H. Auden about an 18th-century Everyman's fall from human grace. Now 30 years old, it is a work that to most is more famed than familiar.

But would that little stage with its cramped access area be able to handle an opera with 10 scenes set in seven places -- such as a spacious London drawing room, a sweaty London brothel and a ghastly insane asylum? Whatever may have been the odds against it, designer Zack Brown swept them utterly aside. Using only painted drops for background -- but lots of them -- he made that Georgian drawing room look right, complete with a stately square visible through the window in the back. Though Brown does not overload with stylistic details, those he uses rings true. Except for the Maurice Sendak designs for "The Magic Flute" all the scenery and most of the costumes this season were Brown's; he made an invaluable contribution.

There had also been doubts about "Rake's" mettle as flesh-and-blood opera. This intellectual tour de force by two of the century's most brilliant artists is intensely cerebral, and in some earlier productions this dimension has seemed to dominate at the expense of dramatic impact. If anything the Opera's production leaned a bit too far in the other direction, letting the action get a little broad and slighting Auden's text in several cases with fuzzy diction. But in the process it proved that "Rake" is plenty human. The Opera can make a real contribution to opera in general by reviving this "Rake" regularly.

Opening this crucial season with Puccini's "La Boheme" may have seemed an easy out; there is no surer way to fill the house (and in this case one in which all orchestra seats had just been upped to $35). Added guarantees were Gian-Carlo Menotti directing, and a budget of $250,000.

But what we got was a fresh, new "Boheme" in which the traditional focus on stentorian vocalizing yielded to an emphasis on characterization. The singing was lovely but not spectacular. Mauceri's conducting was superb. Brown's sets were outstanding. But, most important of all, Menotti had infused the young, and relatively obscure, cast with such dramatic assurance that there can have been few dry eyes as Mimi drew her last breath in each performance.

Two of the other new productions were nothing to be ashamed of -- Donizetti's "L'Elisir d'Amore" and the double bill of Gilbert and Sullivan's "Trial by Jury" and Offenbach's "Monsieur Choufleuri." Perhaps it's time to put the Donizetti to rest for awhile, unless it can be shaped up as "Barber" was. And the double bill seemed harmless, but also frivolous. This kind of opera can be pretty thin without first-rate music.

The Verdi "Macbeth" deservedly took its lumps. The staging was confused and confusing. Feinstein says the idea of doing the battle scenes in slow motion "gave me problems, but there wasn't time to do anything about it." Certainly another mistake was to try so tricky a work on only $100,000. This "Macbeth" should be retired now and replaced in real style in a few years.

"The Magic Flute," borrowed from Houston, showed that Feinstein can choose his loans well, by contrast with the Jean-Pierre Ponnelle desecration of "Traviata" that his predecessors brought from Houston.

Thus, the Washington Opera is at last behaving like a company that knows what it is doing and where it is going.The season was planned and managed both sensibly and imaginatively.

Feinstein dismisses the claims that what he really wanted to do with the Opera was to "build another Met" in Washington. "There is no way that I am going to emulate the Met's operation here," he says. "What we have to look for is a season where we maybe go to 12 operas in perhaps 20 weeks. This season, even, we had more performances than the Chicago Opera. Under our five-year master plan, we will have done a total 17 new productions that we will own by 1986-1987. The 'Boheme,' for instance, is a natural for repetition."

From the box-office point of view, the company seems in good shape. Attendance ran at 94 percent and subscriptions account for about 75 percent of sales. "Now we know we have a public here," says Feinstein, "but the box office just accounts for 36 percent of the budget [$1.36 million]. And as long as we give them high quality, I think we are in good shape in that respect.

"The other major question is fund-raising. The year I took over the Opera it had never raised more than $1 million. This year we've got to find $2.5 million. And it will be some time before we know if we've got it. Everything depends on that."