The 20th century is, even as it draws to a close, difficult to chart. It has produced so many man-made objects - more than throughout all the rest of human history - that it will be years before any museum can refine its design into a single gallery.

Almost defensively, Sue Lambert, the curator of the Victoria and Albert Museum's new Twentieth Century Gallery, says that the display 'is only temporary. The century is not over yet, and, anyway, we hope to get a new building at some point.'

A gallery depicting this century is bound to be an awkward creation. There are still people alive who can remember a time not only before the Sony Walkman and the microwave oven, but also before powered flight. Plenty of people can recall streets lit by gas, milk delivered by horse-carts, commuter trains powered by steam, a time when there were no computers, televisions or refrigerators.

Times and objects have changed so fast that museums have a hard time keeping up, which is why they are often better off worrying about the distant past - measurable, recordable, but unreachable - than struggling with an ever-changing present.

Until recently the Science Museum, the V&A's neighbour, had wonderful displays of model steam locomotives housed in cases that bore equally ancient captions. It was comforting, if not very helpful, to be informed in the late Eighties that those streamlined steam locomotives of the Forties still pulled the express trains out of Waterloo. The museum's captions remained innocently impervious to the fact that steam had given way to an all-electric service at Waterloo in July 1967, the month before the release of the Beatles' Sergeant Pepper.

So how does Ms Lambert hope to encompass a living, breathing, restless century in which nothing is certain? 'By themes,' she announces, an idea which raises fears that the museum is about to turn into a leisure centre or an 'experience' for all the family.

What themes? 'Chairs, for example,' she says, 'or radios; we have a very representative collection of those.'

And so they do. But try imagining for yourself how you might go about representing the history of 20th-century design.

Concorde, a Polaris submarine, or a Saturn rocket? They would be difficult to squeeze into the Victorian confines of the V&A. Try some smaller objects. What about the ballpoint pen, the pocket calculator and the personal stereo? Or, how about plastic bags, flip- top cans and Tupperware, drip- dry shirts, pre-shrunk jeans, and living bras?

The V&A is primarily a museum of the decorative arts; it is more concerned with wallpaper, vases and chairs than anything scientific and technological. Yet a glance around your kitchen is proof of how in this century science, technology and the decorative arts sit cheek-by-jowl, in even the most traditional-looking homes. Here is a 'microchip- driven toaster decorated with transfers depicting wheatsheafs; there is a microwave oven that could double as a helmet in Star Wars. Your kitchen is, in fact, a miniature Twentieth Century Gallery in the making.

Ms Lambert has had to find a way to hone down her choice of objects. So one of her themes is the way we sit. The chair - from steely office perches to a Surrealist sofa by Dali - dominates the display cases of the new gallery.

To pick even one type of chair to represent the century would be difficult, let alone a single example. Should you choose the office chair: at its worst an anatomical disaster, at its best a supportive and beautifully machined piece of furniture? Or should you look instead at handcrafted chairs - Britain has a fine history of such chairs, from the Arts and Crafts guilds at the turn of the century to the contemporary designs of John Makepeace and, at the other extreme, of Tom Dixon.

Or, what about car seats? Cars have become an extension of office and home, and their interiors reflect contemporary design fads; the seats themselves are often the most comfortable you can find.

There is also the avant-garde. The Dutch architect Gerritt Rietveld's experimental Red, Blue and Yellow chair of 1916 is as good a symbol of 20th-century design thinking as any other - say, the tubular steel chairs of the Bauhaus or the work of today's minimalist designers such as Jasper Morrison.

'Is that a prototype of the Rietveld chair?' I ask innocently, staring into a cabinet neatly arranged with clinically designed Modern Movement chairs. 'No]' snaps Ms Lambert. 'Everyone asks that. It's not a prototype; it's an earlier version of the Rietveld chair, which is not the same thing at all.'

Now that the V&A is finally confronting the 20th century, it is reassuring that it should be guided by the spirit of curatorial expertise. Nevertheless, Ms Lambert is in the uncomfortable position - about as uncomfortable as sitting on a Rietveld - of rarely being able to please all her critics.

There is, however, at least one chair in the new gallery that is guaranteed to satisfy. This is a real curiosity, a glass-sided armchair, by the interior decorator Denham McLaren, which is at once decorative and severe, traditional and modern, serious and whimsical. Designed in 1930, McLaren's chair comprises sheer glass sides held together with the kind of chromed bolts you might expect Sir Norman Foster to use in one of his latest buildings.

After this futuristic start, the actual seat is traditionally sprung, stuffed with horsehair and covered with zebra skin. The funny bit is that McLaren left the zebra's mane on the back of the headrest. The chair sums up many of the conflicting desires and contradictions of 20th-century design: our desire to be forward- and backward-looking, decorative and technological at the same time.

But this is a museum-maker's concern, to seek out pieces that symbolise an era. You live in the 20th century: would you give Denham McLaren's chair house room?

The Twentieth Century Gallery, Victoria and Albert Museum, Exhibition Road, London SW7, opens on 22 October.

(Photograph omitted)