LONDON -- In nversation in his book-strewn Kensington Palace study, Prince Charles seems studiously mellow. But in public pronouncements, he says things like: Many developers are more destructive to Britain than the Luftwaffe was; it demolished buildings, but did not replace them with anything uglier than rubble.

Charles has reversed the politicians' practice of being more circumspect in public than in private. A steady stream of shrewd opinionatedness has made him the most consequential member of the royal family since his great-great-great-grandmother, Victoria. Of course, he is not a politician; he cannot be: The (unwritten) constitution forbids it. However, he is trenching on the politicians' turf.

In theory, the modern monarch is part of the ''dignified'' as distinct from the ''efficient'' aspect of the state, with rights only ''to be consulted, to encourage and to warn.'' But by encouraging certain values and warning against others, Charles has become a large part of the nation's political conversation. Because the public is enthusiastic, the political class is tolerating, often uneasily, Charles' deft expansion of the parameters of the permissible.

Charles, 41, is a spirited man in an often dispiriting job. He may be a grandfather before he is king. However, he fills his days by commenting, vigorously, on such matters as environmentalism, architecture (''the built environment'') and falling standards of English usage. Nonpolitical subjects, you say? Not so.

His Philippic concerning architecture began in earnest with a withering (and lethal: The project died) criticism of the ''monstrous carbuncle'' proposed as an addition to the National Gallery on Trafalgar Square.

His is a European sensibility, shaped by cities built before structural steel and elevators, when the necessity of climbing stairs and the load-bearing limits of stone limited most buildings to about eight stories. However, when he denounces London's ''jostling scrum of skyscrapers,'' he also is disapproving of the culture of heroic materialism that capitalism -- and Thatcherism -- celebrates. His architectural, and other, criticisms carry broader, and broadly political, undertones.

The man and the moment met in the 1980s, when three tendencies converged. The mildly liberal social-democratic center collapsed. ''Green'' politics rose from real environmental concerns and from the collapse of the left's traditional agenda. And Thatcherism produced a politics of unapologetic materialism, meritocracy and the economic rationality of profits.

Charles represents the traditional Tory paternalism that Thatcher despises, but he also is a tribune of common opinion, as in his rejection of architectural modernism. He is both trendy green and Tory blue. He can be what he is because she (the one-woman dynasty in Downing Street) is what she is.

His thinking is soft at the edges. It does not often enough collide with toughening opposition, including people who routinely bark ''rubbish!'' when he has, as everyone does, half-baked thoughts. He argues with a diffidence that may betoken want of confidence, the result of not being regularly enough challenged by people who are intellectually undeferential. He subscribes, for example, too uncritically to theories of environmental apocalypse and of the malignancy of economic growth.

When he says man is ''more than a mere mechanical object for making money'' and he deplores the ''fierce obsession about being 'modern','' some Thatcherites hear hostile chords. He is vulnerable to ridicule, preaching from a palace against materialism. But there should always be someone telling the political class that ''no one generation owns the world.'' That message is particularly pertinent to a market-oriented government like Thatcher's.

He wears double-breasted suits with cuffed trousers as badges of conservatism, to complement his temperamental ... what? radicalism? Hardly.

As his architectural tastes are deeply traditional, so, too, are his strictures against the debasement of English, ''the world's most successful language.'' He insists that when ''Middlemarch'' is dropped from school curricula because it is long and demanding, children lose literature's gift of a vocabulary of greatness. When Biblical revision renders ''Harken to my words'' as ''Give me a hearing,'' he asks: By making the words less poetic, do you make them ''more democratic''? He calls that assumption ''patronizing.'' Yet his is an aristocratic resistance to the leveling-down force that is a fact of democratic culture.

The monarchy is in the magnificence business. It supposedly leavens national life with elevating spectacle, stirring sentiments that solidify society, affirming cultural continuity amidst the modern world's whirl of disintegrative forces. Anti-monarchists say monarchy is an anachronistic residue of mankind's primitive past and, with Britain particularly in mind, they argue that it intensifies national inadequacies -- self-deception about residual grandeur and habits of deference toward irrational social hierarchies.

But Charles, not content with a career of merely lending a dignifying presence to things, participates in the shaping of the public mind, which means politics. In 1936, Edward VIII was so shocked by Welsh unemployment he exclaimed ''something must be done to find them work.'' This was considered a constitutional impropriety -- too political. But what is politics?

It is the grand subject of how communities should live, what they should value. Politics is a particularly large subject in the Thatcher era because she regards statecraft as soulcraft; she aims to improve the nation's vigor by changing its values.

Charles' voice is not really raised in opposition, but sounds contrapuntal themes. He is a profoundly interesting paradox: a ''young fogy'' who is both a popular scold and a royal populist. His role is both dignified and efficient.