Critics have wrestled with Verdi's last opera, "Falstaff," ever since its first performance at La Scala on February 9, 1893, when the composer was nearly 80. It was clearly a masterpiece -- the work of a septuagenarian master -- but on the surface it seemed almost un-Verdian.

Here's how Charles Osborne, in his "The Complete Operas of Verdi," described it: "a score whose wit and wisdom are equalled only by Mozart's three great Italian operas: scoring of chamber music delicacy allied to a wide, Beethovenian range of orchestral expression, the magical evocation of forest and fancy in the last scene, and the fantastic pace of the entire opera which seems to last no longer than one sudden flash of inspiration."

The Washington Opera's production does not proceed like a "sudden flash of inspiration." This is a conductor's opera that demands clarity as well as love -- because to do "Falstaff" justice, its extraordinary wealth of detail must be heard clearly. But both musically and dramatically, the Washington Opera is erratic -- sometimes very good and sometimes pretty bad.

Verdi and his brilliant librettist Boito created what in many ways was a new Shakespearean work, by melding the blunderbuss Sir John Falstaff of "The Merry Wives of Windsor" with the older, sadder Falstaff of the "Henry IV" chronicles. Thus both the foolishness and the suffering of this great character are combined.

But Thomas Stewart as Falstaff -- the crude, arrogant, disheveled, devious, obnoxious and utterly appealing knight -- seems to suffer too much for the foolishness to shine.

As Act Three begins, Sir John has been returned to the inn after having been unceremoniously dumped by the ladies in a laundry basket out a window and into the Thames. It is a dark moment. The world is in a sorry state, he reflects, when such a thing can happen to such a pearl of knighthood.

His knightly garb in tatters, his feet bare and even his toupee gone, he looks and moves like an old, weary man. A lackey gets him a chair and brings a tub of hot water in which to soak his feet. He sits down and launches into a grave lament that is as touching as anything in Verdi. Stewart sang it very slowly, with an eloquent lyric line and great richness of tone. It should be noted that his diction was practically perfect -- which, in a Shakespearian opera, could hardly be more important.

But this is the same Stewart who handled the hilarity of the first act in a curiously unsmiling manner, though with some beautiful singing. As he sat at that table in the inn making his plots of seduction he assumed a brooding expression that looked for all the world like Boris in the Clock Scene.

Stewart's characterization at this point was helped not at all by the hyperactivity of Cal Stewart Kellogg's conducting (though Kellogg loosened up later on) and the frenzy of Peter Mark Schifter's staging.

Kellogg raced through the first act as if he were being chased. Crucial details that give "Falstaff" its humanity fell by the wayside. He gave little attention to the subtleties of Verdi's exquisite orchestration. The strings were often covered by the brass and timpani. And much of Dr. Caius' singing, by Leonard Eagleson, was rendered inaudible. Even Stewart's large baritone got lost once or twice.

The scale of the crowd scenes sometimes overwhelmed the opera. That herd of men led by Ford in their search for Falstaff at the end of act two was like a massive police raid.

Also, the slapstick was often excessive. Every time a man made a pass at a woman, he did it by knocking her down and getting on top of her. Really now!

But there weren't too many weak links in the cast, and diction was generally good. The young lovers were a particular delight. They made the last scene a joy. Neil Rosenshein as Fenton opened it and Karen Hunt as Nannetta brought it to its most glowing moment with her gorgeous high notes during the aria out there in the middle of the night with the goblins of Windsor Park.

As Nannetta's parents, Ford and Mistress Ford, Michael Devlin and Patricia Wells were just as engaging. Ford's monologue, especially, is one of the opera's stunning moments, and Devlin was very strong musically and dramatically.

In the delectable role of Mistress Quickly, Joanna Levy was quite broad, in more ways than one, but her humor worked. She lacked only the strong low tones that the part calls for.

And as Falstaff's hapless retainers, Bardolph and Pistol, Richard Croft and Saverio Barbieri were just fine.

It was not a polished "Falstaff" most of the time, and could probably have profited from more rehearsal. But there is every reason to expect things will fall together better in successive performances. FALSTAFF -- At the Kennedy Center Opera House, this Saturday and November 10, 14 and 19.