Once in a great long while during a Vincent Scully lecture, the sensitive ear can detect a tiny pause on the way to a "whereas" or a "nevertheless." This is a comforting discovery, for it is the only outward sign that, like other human beings, Scully must, from time to time, breathe.

In his classes at Yale on architecture and art history--which are some of the most popular classes at Yale--Scully forbids note-taking, on the theory that his students should get as swept up in the fervor of the moment as he is. The rules aren't so strict in his current standing-room-only lecture series at the National Gallery of Art, but the passion and the pace are, as ever, full-blast.

Not even the podium is allowed to stand still. Scully insists on beating it like a tom-tom whenever the fancy strikes him, and the PA system carries every tap of his finger to the farthest corner of the East Building's 450-seat auditorium, back where the standees are peering over shoulders for a glimpse of him.

He speaks with only a tad less intensity from the corner of his room at the Hotel Washington on a snowy pre-lecture Sunday morning. He fiddles with the blinds, squirms in his chair and nearly knocks a lamp off a side table with a routine hand gesture as he inveighs against the 20th-century Germanic school of modern architecture and "all those silly rules--this was right, that was wrong, you couldn't do this, you couldn't do that--which were ridiculous and pompous and joyless and without wit and without irony!"

Scully recalls that he was "brought up to believe that Washington's classical architecture-- especially its 20th-century classical architecture--was ridiculous. But now I think it's wonderful. I like them all. Thank God they weren't built by the Bauhaus! Imagine Washington with that character!"

At the mention of the word "Bauhaus," his hand collides again with the lamp, and his fervor seems at odds with his natty Ivy League attire, in which only a red plaid tie breaks the general pattern of brown and beige.

Once, during a Yale lecture on the firm of McKim, Mead and White, Scully showed a sequence of slides of the old Pennsylvania Station in New York and spoke rapturously of its space and grandeur, only to bring on a slide of the same columns smashed in half, with wrecking equipment all about them. "Everybody was absolutely stunned," a student recalled in a 1980 New Yorker profile of Scully. "It was unbelievable. For a moment, Scully's voice broke--he choked, and couldn't go on. Then, quickly, he said something about how it was 'obscene.' He sort of barked out the word 'obscene.' Then he continued with the lecture. But the class was in a state of emotional collapse."

Such memories, and the word of mouth spread by Scully's many former students, go a long way toward explaining the hefty turnout for his six Sunday lectures on French architecture at the National Gallery, and his single lecture on modern and postmodern architecture at the Museum of American Art.

A slide projector, in Scully's custody, becomes a musical instrument working in perfect harmony with his voice. The pictures never pause for his words. His words never pause for the pictures. And if something should go amiss mechanically, Scully, looking devastated, apologizes profusely--as if to say, "This is not how it should be. We know how it should be, don't we?"

Things are more likely to go amiss for Scully than for the average lecturer because he works with two slide projectors. Thus his audience is always looking at two images, and in the juxtapositions--by turns outrageous, powerfully revealing and all but baffling--the essence of Scully is to be found.

A Mayan temple faces off against New York City's Gulf + Western Building, and Scully, arms waving in the air, unabashedly summons his audience to appreciate "the same upward stretch" in both. Or we see a classically Greek monument, pillared and precise, next to a hulking specimen of Pueblo Indian architecture, and Scully talks about how they relate to the mountainous landscapes in which they both stand. He speaks of "the Greek will for geometry and human order." The columns at Delphi "stand out against nature and seem to defy it," he says, in contrast to the "much more normal pre-Greek or non-Greek way in which monumental human architectures are seen emulating nature."

A listener may not follow all the connections Scully is making, but the words and images flow so quickly that it is hardly necessary to linger on a point of confusion. And if Scully occasionally seems to be heading in more than one direction at once, the same could be said about architecture itself, of whose contemporary trials and errors he has been sometimes a detached critic and sometimes a helpless captive.

Scully was born in New Haven, Conn., in 1920, the son of an Irish Catholic Chevrolet salesman who was "totally without malice" and never went to high school; and of a formidable, artistically sensitive woman who developed her coloratura soprano voice for a hobby and sang so loud that, as Scully once said, "It literally hurt my ears, and the dog would howl."

The confrontation of lowbrow and highbrow has been an ongoing thing in Scully's life. He was a townie who entered Yale at 16 on a full scholarship, then waited on tables to help pay expenses, "and hated it."

After Marine Corps service in World War II, Scully returned to Yale as a graduate student in art history, and he has remained there ever since, to fill succeeding generations of students (future architects and otherwise) with his rudimentary passion about what humans have been trying to say with their buildings, from ancient Greece to now.

Ancient Greece became something of an obsession for Scully in the 1950s and early '60s. And with his head up in the Olympian clouds, he says apologetically, he wasn't as attentive as he might have been to the course of modern architecture and its consequences for city dwellers the world over.

Insofar as he had thought about Le Corbusier's vision of the modern city--with awesome towers engulfed by open space--he thought it was "heroic, splendid and glorious and so on."

But in 1963, after finishing his book "The Earth, the Temple, and the Gods," Scully went back to Athens and found its modern metamorphosis deeply depressing. The same year, he drove down Interstate 95 for a lecture at the University of Virginia, and looking out through his car window, he saw that "everything I'd accepted as the way things naturally had to be was wrong. All of a sudden, it seemed to me that modern architecture was destroying the world."

In his home town, meanwhile, the urban-renewal wars were on. One of Scully's sons had gone to work for the architect Louis Kahn, certifying that most of the threatened houses of "the Hill" neighborhood were structurally sound and therefore salvageable. Scully himself took part in deciding the fates of two old New Haven landmarks: the Post Office (a Beaux Arts structure built around World War I) and City Hall (a Gothic Revival structure built around the Civil War).

Support for each of these buildings was vociferous, but strangely, almost no one wanted to save both.

"We got two sets of letters and they all depended pretty much on the age of the writer," says Scully. "Many of them from Yale graduates--those who had gone to the architecture school way back in the Beaux Arts days--would write in and say, 'Save that beautiful post office, but let that silly Gothic Revival City Hall go.' Those who came in later--and I'm sorry to say that people of my generation were partly guilty of this--who had been taught that the Beaux Arts was anathema, would say, 'Let that silly Beaux Arts building go, but save that Gothic one.' So if we paid attention to changing tastes we'd lose everything sooner or later. There's so much greed around all the time. There are so many pressures around."

(In the end, City Hall was partly demolished, while the Post Office remains intact and is now a federal courthouse.)

The New Haven experience left him with a lasting caution about the practice of having committees decide, on esthetic grounds, the fate of imperiled buildings. Scully is particularly uncertain about one such current controversy, surrounding the fate of Lever House in New York City.

"It was the first of the curtain-wall skyscrapers on Park Avenue," he says, "and a lot of people, including myself, have really seen it as the villain which began to destroy the urbanism of New York, the urbanism which was based upon the older traditional classical sense that the street was a good thing, that you defined it with solid buildings, you defined streets and squares, you had lower floors which were shops, you had something for the pedestrian. It's the whole way that modern cities developed. But the International Style didn't value that at all. They didn't understand it. They had what I used to call a cataclysmic urban design: Tear everything down and start over with freestanding buildings on legs in open lots--that's basically what it amounts to. And Lever Brothers was the first one of those injected into New York, and it began a destruction of Park Avenue."

Incidentally, he adds, it was a very different building when it went up in the 1950s compared with now, because then "it was the single curtain-wall, shiny glass and plastic object, in a brown setting of masonry, and indeed it was conceived of by its architect as something which would be a precious object seen against its opposite. But as time went on, all the buildings around it imitated it."

Now a developer wants to tear down Lever House and build a bigger skyscraper on the site.

"What do you do with this building, which is in many ways urbanistically a villain?" Scully asks. "A number of people have signed a letter to save it, and I think I'd like to save it, too. It's an object lesson, maybe, in what not to do in the city, but it is a historical document . . . and I deplore this business of smashing everything down every 20 or 30 years."

However, he has no qualms about Maya Lin's design for the Vietnam Veterans Memorial. "That girl was a student of mine. I've visited the memorial several times . . . I've always been moved by it and by her conception."

To the complaints of some veterans' representatives that the memorial resembles a latrine, Scully counters: "I don't see that. It brings Lincoln and Washington into perspective in relation to this war and this experience. It couldn't be more noble from that point of view, and it couldn't take in more of the grandest part of the Mall than it does . . . It's magnificent, magnificent. She's fantastic."

He is even more energetic in defending the work of his former Yale colleague Robert Venturi, one of the conspicuous figures in American architecture's current revival of enthusiasm for arches, shingles and symbolism. Venturi's design for the Transportation Square project on Maryland Avenue SW would have been "one of the most important modern buildings in Washington," says Scully. But that project and Romaldo Giurgola's plan for the American Institute of Architects were never built because, according to Scully, "they didn't square with the very hermetic and intolerant esthetic of Gordon Bunshaft," an influential former member of the Commission of Fine Arts. "And Bunshaft was the guy who designed Lever Brothers," Scully adds trenchantly. "Talk about turning the other cheek!"

As a member of the Yale faculty, Scully has been much affected by the theories of his colleagues in the fields of literature and linguistics. Thus when architects refuse to acknowledge the influences Scully has identified in their work, he points to Harold Bloom's writings on the "anxiety of influence" among poets.

"Art seems to come out of art," says Scully, "even though artists don't like to admit it." Frank Lloyd Wright, he says, never credited the influence of American Indian architecture on his Taliesin West project in Phoenix, but Scully is convinced the influence is there nonetheless. "Most of us," he says, "would like to believe that artists are somehow in touch with some kind of divine force and are answering fundamental questions of human life--which they do, but they have to do it through an alchemy of form, and that's the nitty-gritty. How do you get those forms? That's what everyone fights about all the time."

The process by which a critic of architecture, like Scully himself, abandons old tastes for new ones strikes him as no less mysterious. Asked why modern urban design began looking sinister to him in the early '60s instead of, say, the '50s or '70s, Scully replies: "It's always like that. We only see what our preconceptual structure permits us to see. We always see everything from within blinders." But from time to time, people have an esthetic response that "short-circuits our preconceptual response."

That's why the esthetic response is "the moment of uttermost sanity in human life," he says, his wide eyebrows arching high.

And yet, because tastes ebb and flow, architecture can be a cruel field.

Many of the splendid American houses of the 1880s--in which vast shingled exteriors somehow managed to encompass turrets, porches, gables, round windows and other acts of seeming craziness--were later demolished by owners who saw them as hopelessly outdated. But as Scully has written: "They were the freest and . . . among the most generous forms that the United States has yet produced. No American living . . . can look back upon those houses without some nostalgia, disappointment or even sorrow. They promised a great deal for American life which has not been fulfilled."

And just as buildings can be demolished, so can architects.

"I can remember," Scully says wistfully, "when I was first teaching at Yale in the late '40s, there were a whole bunch of old gentlemen who had been trained in the Beaux Arts--the great academic classical tradition--who had tenure so they couldn't be fired, but they didn't have any students. Nobody paid any attention to them. Now everybody wishes they were around again!"

Scully will deliver the last two Sunday lectures in his series Feb. 20 and 27.