US realist Alex is coming to England, but what will we make of him? asks Andrew Lambirth
Alex Katz is almost unknown in Britain. A realist painter born in New York in 1927, he studied art in his native city and in Maine, mingling the influences of town and country - a pattern which has continued to inform his work. Katz has been a name to conjure with in America since the 1960s, when his distinctive style of placing figures frontally on the canvas in simplified and flattened arrangements began to be noticed.

At that time, the New York art scene was still very much dominated by the Abstract Expressionism of Pollock, de Kooning and Rothko, and the abstract art that grew out of it. The only viable alternative was Pop art. It was a substantial achievement to be recognised at all as a realist painter. In London we are only now celebrating Katz properly. In January an exhibition of 26 of his paintings opens at the Saatchi Gallery; the book of the show is however already available.

Throughout his painting life, Katz has restricted himself to three subjects - the landscape (preferably in close-up), the portrait of the individual, and the group portrait. It is the last category which perhaps best typifies his work - or at least its most public face. Katz occasionally paints the nude for instance, but the results are never exhibited. Katz regards his subject as having been given to him at the age of 20, and he's not about to renounce it. Instead he rings endless changes on certain fixed ideas.

He is the master of variations on a theme. The same characters appear in similar scenes. As he once said: "They're in roles. I'm the director. That's how it is." On the other hand, he is prepared to look at what he does in purely formal terms. In a recent interview, he identified his subject matter singly as "the outside light".

Katz does have a tendency to repeat the same figure in the same painting. Much like a film director, he is going for different takes within a single picture space. He likes doubling up.

Another spin on this is his habit of showing one of his own pictures, or part of one, within another painting. You might expect these static figures to have a classical weight and solidity, yet they are curiously two-dimensional.

If Katz' figures resemble cardboard cut-outs it's because he does not aspire to serenity or ideal beauty - he is not making ordinary people into mythic beings. These images remain two-dimensional because they are what they are - images: painted copies of people. There's a piquant honesty here, as well as a nod towards post-modernism.

There is a wealth of thought and art history underpinning these paintings. Katz admits to being fascinated in the early 1950s by the work of Piero della Francesca. Certainly some of the calm organisation of flat, yet realistic shapes, so typical of della Francesca, can be discerned in Katz' work. He also, perhaps surprisingly, talks of the influence of Pollock, Rothko and Kline. They apparently brought him to the painters of the Baroque such as Tintoretto, Rubens, Veronese.

Katz is nothing if not eclectic in his art historical references. Of course, the Baroque style was chiefly characterised by movement, and most of Katz' paintings are notable for their stillness, the figures frozen, the moment arrested. However, the recent paintings of blossom, or foliage in a wood, all vertiginous movement, do refer back to this earlier interest.

The Red Band is typical of several Katz strategies. It makes high art references, in particular to Rodin's Thinker, and it features the same woman twice. A double portrait in different positions, it raises the issue of identity - of twin or doppelganger, of your other half existing somewhere in the world. Katz often paints his wife Ada, as he does here, though more to glamourise her than highlight the domestic virtues. If the vision is ostensibly fantasy-prone, it's also strangely empty. The stylisation somehow allows Katz an abdication of commentary: the meaning is as flat as the image. Make of it what you will.

Katz makes paintings of heroic scale which are near-naive in their apparent lack of inflection and subtlety. Details are subjugated to the overall effect. It's a kind of formalisation: rhythms are more important than the signs of evident brush-strokes. This is "optical" painting, but of a generalised kind. Katz portrays strictly what is seen, not what is felt or otherwise hidden from view. He does it boldly, aiming for an in-your-face directness. He draws on the mass media images of consumerism, particularly the billboard and hoarding. From these sources come the flat areas of largely unmodulated strong colour, and the severe cropping of the image which distinguish his work. Yet Katz also makes these devices serve his purpose to make fine art: he holds down large areas of colour and vivifies them unexpectedly. In Red Coat the right-hand edge of the canvas slices through an eye and cuts off the lips, but what intensity this confers, what focus!

These paintings are reminiscent of the snaps in a photo album, a gauge of their accessibility rather than the distancing expected of high art. Katz did in fact make considerable use of photographs earlier in his career. Despite his ability to use the kind of material familiar to Pop art, his work is not a classic Pop celebration of consumerism.

He is not really a Pop artist; his attachment to that group remains only tangential. His interest lies in transforming his subject matter in a way that would have seemed unnecessary to Warhol, for instance.

Take a picture like Blue Umbrella (1972). Katz paints his model in a self-sufficient little world, neatly and securely enclosed (at least compositionally) by the umbrella. The girl is as enigmatic as the Mona Lisa, though perhaps without that beauty's depth of human subtlety. Each raindrop which veers across the picture plane is painted individually, and differently slanted. This is not programmatic painting of the obvious kind, dealing in simple repetition. But look at the eyes. Eyes assume considerable importance in Katz' work. Sometimes he paints only one, but the composition will revolve around it. Traditionally, the eye is supposed to be the window of the soul. In Katz' paintings, the shutters are firmly down.

Legend has it that Alex Katz single-handedly reconciled the two great opponents in the post-war art debate - abstraction and realism. Even disregarding such obvious forerunners as Edward Hopper, it is rather too much to lay at one man's door. How has he assumed this heroic status? Perhaps the certainty and consistency of his art, its simple rigours, have played a part. Whatever, it's a fact that Katz is equally popular in America with critics and public alike, though there are exceptions, of course. Not everyone takes kindly to what can be seen as a reduction of humanity to a Disney-like formula.

Robert Hughes, the combative art critic of Time magazine, has called Katz "the [Norman] Rockwell of the Intelligentsia". He also refers to what he sees in Katz' stereotypes as "the pharaonic prettiness of his art". The million-dollar question is will Katz be as popular here?

Recently the critic of a Sunday newspaper stated unequivocally that we must not allow the tastes of the public to diverge so far from those of the aesthetic commentators as we have during the age of modernism. (In other words, no one really likes modern art - unless it be Dali - except the critics.) Perhaps Alex Katz is the answer?

There are however several artists at work in England whose aims and achievements are not so different from those of Alex Katz. (That's one possible reason why Katz hasn't previously been promoted here; we have our home-grown versions.)

In the realm of still-life, Patrick Caulfield excels at reconciling the abstract and the particular. He is the poet of the naff bar or pub interior. Euan Uglow paints the nude in a way which deals with specifics and also transforms the image into facets and flat planes. While in terms of figure groups, Peter Blake presents Tarzan and family in uninflected glory. These artists paint pictures which don't have any literary meaning as such, but which deal with ideas - pictorial ideas. They hold that in common with Katz.

We may be forgiven for thinking Katz all polished urbanity when he ventures a statement like "I think nature's just a vehicle for art." He avowedly prefers style to content.

Although he cannot prevent the curious viewer from wondering what's going on in these pictures (who said what to whom, and why?), Katz does his best to focus your attention on the surface rather than on any psychological depth. The curious balance that Katz maintains between the formal aspects of the work (the composition, the play of light, the arrangement of forms and especially of colours) and its meaning (or lack of it) creates a stasis which allows the picture simply to exist as it is. What you see can be what you get.

Again in Red Coat, there is an inward-looking, soul-searching quality to the painting. Though apparently looking out, it may be that this woman is engaged in self-questioning. But surely that would be a narrative of sorts? Better forget it. Ada Ada is another double portrait, but it's not an identical repetition. Is one image a copy of the other? Or a further attempt to get it right? Is one better than the other? (And is that important?) What is important is the extraordinary intensity of the colour which provides a background for this unexplained but somehow mysteriously iconic image.

January III contains a face inserted between two halves of a copy of another painting, Winter Landscape, to form a sort of triptych on one canvas. It's a typical Katz reworking of other images, and looks a little like two scenery flats or screens trying to shut out some giant looming wicked witch. Here we have woman pitted against nature, but there's no intended comment and no resolution of an issue. Meaning denied as usual. The lattice of branches has an much relevance as the model's big red mouth: they are equally important to the structure of the picture. The movement implied by the interweaving of the trees is checked by the imprisoning fog; stillness is maintained.

There is something disconcertingly inhuman about these paintings, which no doubt accounts for part of their power. Interestingly, Alex Katz often calls his own work "cool" or "cold". It's as if he doesn't want to encourage a warm, not to say passionate, emotional engagement with his art. Yet paradoxically, that is precisely what he achieves by being so popular. People engage with his art, they love it. It would appear that Alex Katz thrives on such contradictions.

In 1977, high art made amends with low art: Alex Katz went out on the street. He designed a massive billboard for Times Square, featuring 23 heads of young women. What he had borrowed from the popular arts of film and advertising he now gave back. Appropriately enough, the billboard was not painted by Katz himself, but by a professional sign painter. His art had in one sense come full circle

Alex Katz is at the Saatchi Gallery 15 January to 12 April 1998. A hardback book on the artist and his work, edited by David Sylvester, is available now at the gallery and art bookshops, price pounds 29.95