WATCHING Israeli children being issued gas masks on television forcibly reminds any Londoner who was a child here in the pre-world War II period (as I was) of our own encounters with the gas mask. Whatever dread there was in our parents' hearts, for five-year-olds the cardboard boxes containing rubbery-smelling snouted masks with adjustable straps that allowed us to transform ourselves into comic monsters made very good presents, all the more acceptable for being unexpected and requiring no thank-yous. We can recall them affectionately, of course, because we never had to use them; they remained toys until we grew bored with them and they perished, forgotten till now. We can only pray the same will be true for the children of Jerusalem, Tel Aviv and the West Bank.

Not much of pre-war London lodges in my memory, though something stirs when I read the poet Louis MacNeice's Autumn Journal:

. . . Hitler yells on the wireless,

The night is damp and still

And I hear dull blows on the wood outside my window;

They are cutting down the trees on Primrose Hill.

The trees Louis MacNeice heard being chopped down on Primrose Hill have grown again, though he would not have recognized the view from the top of the hill, from which London, on a clear night, can now look almost like L.A., with its rings of sparkling lights and brilliant towers. But much more than the architecture has been changing in London. A whole pattern and way of life that seemed an organic part of the city's center disappeared quite suddenly in the 1980s. For two centuries the main cluster of the newspaper and publishing world was conveniently centered on Fleet Street, Holborn and Bloomsbury; from the time I started in publishing and journalism in the 1950s, it was in offices in Great Russell Street or Bedford Square, Shoe Lane, Lincoln's Inn Fields, the Gray's Inn Road.

Living in Camden Town, I could, and did, bicycle to and from my job every day. Not many journalists bicycled, but writers, editors and journalists did work in close physical proximity, used the same pubs, wine bars and restaurants, dropped into each other's offices, went to each other's parties, swapped gossip cosily twice a day. The City and the Law Courts, with their useful stories and contacts, were both close at hand. Suddenly, with the coming of the new technology and Rupert Murdoch's breaking of the old print unions, this tradition -- this whole world -- was exploded. The newspapers moved out to Wapping, Chelsea Bridge, Marshall in the East End, Kensington High Street. Not many of the publishing houses and literary agencies are left either: My own agents have moved so far up river that it's rumored they can be reached only by hydrofoil.

All this has been bad news for writers. Dropping in on your publisher, or to see the literary editor of a newspaper or magazine, or chat with your agent, was a comforting activity, and useful for all concerned. When I was literary editor of the New Statesman in the 1970s and the Sunday Times in the 1980s, I relied on seeing my contributors face to face regularly, looking through the catalogues and the books with them in an easygoing way, sitting down to talk over their copy; we could go out for lunch, or get a cup of tea, without it being a major performance.

My impression is that literary departments are no longer run like that. Contributors are less likely to come in to the office, because it is simply too remote. So reviews are posted or faxed, and talk is by telephone. I have not been to the offices of any of the three literary editors I have lately written for; in fact I have come face to face with them only at large, formal parties given by their employers in public rooms miles from the places where they actually work. I feel I don't know them, and they don't know me. They could be in America, or Australia.

It's sensible to use new technology, of course, but fragmentation and impersonality are not the most propitious conditions for the literary life. And who would have predicted that the new technology actually means less efficiency? Copy dates are much earlier in the week, and the good old practice of letting writers correct proofs of their reviews, often done in person in the office, is virtually abandoned. Once the newspaper itself thinks this attention to detail doesn't matter, you risk breeding contributors who think mistakes don't matter much either; if the editor doesn't care, why should the writer? It's only a paper. Bastions of Learning FOR MANY writers, the twin poles of London are the British Library and the London Library, both mercifully still in the center. The British Library has a few more years to go in the British Museum in Great Russell Street, but is due to move in 1996 to new buildings going up next to St. Pancras railway station. They may be more efficient -- time will show -- but they are certainly not beautiful.

The wrench for readers accustomed to the present Reading Room will be painful. It is not just a sentimental attachment to the spot on which generations of readers -- Dickens, Bernard Shaw, Marx et al. -- have educated themselves; there will surely never be such a satisfying place to work as beneath that vast airy dome, which allows fancies to fly up yet contains them within perfect classical proportions. But when lamentations are voiced on this subject, a populist grumble comes back that it was always too difficult to get a reader's ticket anyway. Tickets are not paid for, but you must prove scholarly need. The late Joe Orton has a line in his play What the Butler Saw which describes a certain woman as being as difficult of access as the British Museum Reading Room; it usually gets a laugh. Yet when you look round the desks, you wonder about this exclusivity. Half the readers look as though they might have stepped out of an Orton or an early Pinter play. Some of them have clearly come to sleep, others to write their novels; some leave piles of paper rubbish on the desk while they wander aimlessly about. You ask yourself how they ever got their tickets. One of them may be a genius, of course.

The London Library, set in St. James's Square between Pall Mall, Piccadilly and St. James's Street, amid the gentlemen's clubs, is a very different matter. You need

80 for a year's subscription, unless you choose to become a life member, which will cost

2,000 for anyone under 25 (the amount falls with each five years of your life). The library is a great British institution, dear to the hearts of its users -- Antonia Byatt set the first scene of her best-selling novel Possession in it, and David Hare made the heroine of his latest television play, Heading Home, work as a librarian there. It has over 7,000 members, a surprising number of whom know one another, so that on any visit you may reckon to see half-a-dozen friends, which is sometimes a mixed blessing. F.R. Leavis, the Cambridge literary academic who spent his life excoriating the literary establishment, warned his pupils against the dangers of joining the London Library; but it wasn't the aroma of privilege he objected to, I suspect, so much as the sense of enjoyment. It is a place in which people are seen to take intense pleasure in books.

The Library celebrates its 150th anniversary this year. It was founded on 3 May 1841 at the urging of Thomas Carlyle, and opened in two rooms in Pall Mall, with 3,000 volumes. Today it houses something like a million. You can browse in stacks with steel floors, work in the elegant reading room on six days a week, take books home with you or have them sent, and keep them as long as you like, or at least until another member puts in a request. No other library offers quite this range of services, and the membership is always growing.

The premises have been enlarged several times already, and need further extension. Still more important, all the library's functions must be brought up to date, and in line with other libraries, by being computerized. This means raising

3 million, and an appeal is being launched to coincide with the anniversary celebrations. Members will cough up, no doubt, but big benefactors are needed. There is to be a specially designed silver medallion; and John Wells has written a history of the library, Rude Words, to be published in the summer, which will undoubtedly be very funny, and probably a little mocking too. The Streets of London THE LONDON Library is clearly shown and named on the London map of 1862 I've been using for the past four years. "Using" is an understatement. I have lived in this map throughout the time of researching and writing a book about Charles Dickens (a founder member of the Library) and his secret friend Nelly Ternan, whose relationship spanned the years 1857 until his death in 1870. Stanford's Library Map of London and its Suburbs for 1862 is a magnificent thing, 2,224 sheets covering London and the suburbs on a scale of six inches to the mile. (Mine is not an original, of course, but a fine reissue put out by the Guildhall Library.)

Dickens was a famous and indefatigable walker of the London streets, and he put his knowledge to use in his life as well as his work. He thoroughly understood that you could change your identity by moving from one district to another, and thoroughly appreciated the habit of his many friends who kept more than one establishment. Dickens usually had at least three: a family one, a bachelor one and one for Nelly (not to mention various houses up and down the Hampstead Road in which he kept his old mother, his widowed sister-in-law, etc.). Following his movements on a map helps you to see how he did it, and Stanford's London has become almost more familiar to me than the real one outside.

I have felt quite annoyed to see that the street plan round the Lyceum theatre in Wellington Street, opposite which Dickens kept his bachelor flat, has been changed by the cutting of Kingsway and the Aldwych. I'll forgive Charing Cross station for being there, because it was built in 1863, in time to be of use to Dickens for his many trips to France. But where is Tavistock House, where the Dickens children saw their schoolroom turned into a theatre? Where is St. James's Hall in Piccadilly, where he did so many of his London readings? Where is the house he gave Nelly, near Mornington Crescent? That whole area, once pretty, has been ruined first by the railway lines eating away houses and private gardens, most recently by the zeal of the post-war planners, who razed what was left of the streets and squares in order to put up their monstrous blocks.

But I discovered, to my joy, that the "Park Cottage" where Nelly was living with her family in 1857, when Dickens first met her (and which he condemned as unsanitary), is still there, bearing the same name. And the house in which Mrs. Dickens settled after the separation is also still standing: In fact I pass it every day, since I live only a few doors away. Sometimes I feel guilty for living so much in the past, but it's something London tempts you to do; and the present is not the happiest place to inhabit in these early months of 1991. Claire Tomalin's most recent book is "The Invisible Woman: The Story of Nelly Ternan and Charles Dickens," due out this spring.