With adulthood thrust upon him

January 10, 1984

Though subsequent generations have tended to see them as refined to the point of artifice, Agnolo Bronzino's portraits were praised by his contemporaries for their ''lifelikeness.'' Looking at ''Giovanni de' Medici at Eighteen Months,'' one finds it easy to see why. But this engaging child portrait is exceptional in Bronzino's work.

There is little here of the remoteness, the lean and smoothed idealization, found in many of his adult portraits. S. J. Freedberg's statement that this 16 th-century Florentine painter ''altered human presences into improbably pure statuary,'' while perhaps justifiable as a description of figures in his religious and allegorical pictures, is only half true of his portraits. And of ''Giovanni'' it is completely untrue. The fat little son of Cosimo I - the first Medici ruler of Florence and Tuscany to style himself ''Duke'' - is surely recorded with authentic realism and directness.

Born in September 1543, Giovanni was soon described as ''beautiful and plump'' and ''like an angel in paradise.'' When he was four he was ''the handsomest and happiest (boy) that ever was. . . .'' Clearly his parents were very fond of him, as well as confident of his dynastic promise. A later portrait by Bronzino of his elegant and sophisticated Spanish-born mother with her arm around him (ca. 1546) certainly shows him growing up into a personable, small boy of obvious brightness and vitality.

But to modern eyes, perhaps, ''Giovanni at Eighteen Months'' does not immediately suggest the ''angelic.'' His pudgy hands clutching the unfortunate goldfinch, his old-mannish portliness, his overfed chuckle at odds, somehow, with a too-knowing glitter in the eyes, suggest he might only too easily develop into a ruthless tyrant - or, at least, a pugilist. One feels, encountering his visage on the walls of the Uffizi in Florence, that here indeed is a child of forbidding mien!

It seems on further acquaintance, however, that this initial reaction is not just. His subsequent short history shows him to have been precocious, cultured, and intelligent. At 17 he was archbishop of Pisa. He was a prodigious writer of letters. He studied under a humanist called Antonio di Barga.

His appearance as a baby probably seemed to Bronzino more or less faultless. Given that the artist was prone to a certain courtly flattery with regard to his patron's family, it must also be taken into account that plumpness in a baby was , in that period, a positive ideal. You only have to look at the chubby little boys depicted by artists as the infant Jesus, or John the Baptist, or as ''putti'' representing either fancifully winged angels or attendants of cupid, in Renaissance art, to realize that slimness was not considered beautiful. Chubbiness was far more desirable. In everyday life, sadly, many children fell short of this ideal. So when a child - like Giovanni - was actually robust, laughing, energetic, and as rotund as a plum pudding, there was cause for considerable rejoicing.

Generally, Bronzino - who was at his peak in 1545 as court painter to the Medicis - combined in his art the ideal and the real, with the former dominant. Few of his contemporaries could endow religious or secular pictures with his rarefied, idealized perfectionism. But he was also unrivaled in his meticulous enjoyment of textures and physical details. In this respect his paintings seem to hark back to the kind of tactile discrimination found in early Flemish oil painting - to delight in differences of feel in materials, among brocade, jewelry, hair, skin, for instance.

It would be misleading to conclude, however, that his religious paintings and allegories were of an entirely separate order from his portraits, with the one idealistic and the other realistic. For one thing, he often incorporated portraits into his religious paintings. And also, almost all of his portraits (even the sparkling picture of another child of Cosimo I, his little daughter Bia) are invested with a fair degree of cool, flawless clarity that forbids intimacy. There is in them an element not so much of arrogance as unquestionable superiority.

In displaying his patron-sitters in a condition of such unapproachable distinction and high breeding, he was giving them exactly what they wanted, of course. Describing his portraits, Charles McCorquodale has written that Bronzino endowed them with ''that remote, self-absorbed stillness where, despite the irresistible tangibility of every detail . . . personality has begun to withdraw.'' This was perfected ''to the point where nothing was permitted to remain that would disturb the persona constructed exclusively from immaculate externals.''

The different character of ''Giovanni'' lies in its evident spontaneity and (for Bronzino) almost ebullient naturalism. This laughing child of wealthy and important parents is certainly not deprived of the trappings of opulence. His costume and pose make him look much older than a mere 18 months. Status, class, and adulthood have been early thrust upon him. But in spite of this, he has not been elevated by the painter into a symbol. He remains accessible to the viewer. His baby laughter has defied Bronzino's artistic defenses, making it impossible for him to construct any kind of mask. Style does not intervene. And Bronzino shows himself capable of a remarkable straightforwardness and, without artifice, a genuine warmth.