A walk in Bloomsbury

When I set out on the Bloomsbury walking tour, I expected to be fed Virginia Woolf and E. M. Forster anecdotes and tales of Karl Marx in the British Museum. Two hours later I was happily sated by the habits of the plane tree and memories of such earlier Bloomsbury denizens as - believe it or not - Pocahontas and Edgar Allan Poe.

Such are the surprises in store for those who sign on with London Walks, an intensive, inexpensive, and altogether invigorating method of exploring a city that is, after all, meant to be seen on foot. I might have spent that bright cold late autumn Sunday another way if I hadn't sneaked a hurried look at The Times on the three-hour, 21-minute Concorde crossing from New York the day before. Listed under ''Today's events - Walks'' was a two-line notation: ''A London Village - Bloomsbury, meet Holborn Underground, 11.'' Three other walks were listed, Hampstead, Westminster, and Jack the Ripper's East End, but I was drawn to those upper middle-class bohemians, the Bloomsbury Group.

We met outside the Holborn tube station, a dozen assorted Americans, Canadians, and Londoners, and a guide named Ann Murray, who said she had devised the Bloomsbury tour eight years ago. We each handed over (STR)1.20 (about $2; students pay (STR)1; children under 16 are free) and at 11:10 a.m., having allowed for late arrivals, we set out behind our briskly striding leader. London Walks (139 Conway Road, London N14 7BH, phone 882-2763), generally led by part-time actors like Mrs. Murray, are friendly but fast-paced affairs. This enables you to finish an 11 a.m. tour at 1 and still have time for a bite of lunch and an underground ride to a 2 p.m. tour - if the mind and constitution can absorb it all.

Down a narrow lane away from the busy Kingsway we paused to look onto Lincoln's Inn Fields. ''We are around the corner from Sir John Soane's house,'' said Mrs. Murray. ''You must come back on your own and see how this gentleman - he was a great architect - lived at the start of the 19th century. He left such an excellent collection of art and artifacts, ''The Rake's Progress,'' by Hogarth for one thing, I think the British Museum is jealous. And there is no charge.''

In a city rich with parks and squares - 712 in number, to quote our dashing leader - Bloomsbury was not cheated out of green space. In fact the tour was something of a hopscotch game from one park to the next, first to Red Lion Square where a new bust of Bertrand Russell lay in the chill shade and pigeons huddled in the sunlight as though listening to the spiel; then to Queens Square where a sheepdog lapped at a water pump beneath a sign ''Unfit for Drinking'' and we peered across to St. George the Martyr, also known as the Sweep's Church because the children of chimney sweeps once received free meals inside.

Most of the squares and parks looked green and timeless, but here and there the surrounding 18th- and 19th-century row houses were broken by modern angular buildings - the work of the Luftwaffe. ''The Nazis,'' said Mrs. Murray, ''went for the railroad stations north of here, but they got the Bloomsbury squares instead.'' Bloomsbury's noble trees seem to have survived the bombs and time. Everywhere we walked the pavements and lawns were blanketed with floppy big leaves the size of place mats. ''They are plane trees,'' we were told, ''mostly from the 18th century. We call them the Lungs of London because their chlorophyll keeps the air clean.''

Between Red Lion Square and Queens Square we rallied round a recumbent statue of none other than Pocahontas, the Indian woman who had, as every American schoolboy knows, saved Captain John Smith's life in colonial Virginia. ''She married John Rolfe, a Jamestown settler, and later moved to London. She was absolutely beautiful - people just stood and stared at her. But Pocahontas couldn't stand the English weather and died here, at 22. She is buried in Gravesend.''

On Southampton Row, an ordinary commercial street, we were told that Edgar Allan Poe had been a childhood resident. ''Poe said the melancholy of the street suited him,'' Mrs. Murray went on. ''He spent 12 early years here and lived on Russell Square as well.'' Around the corner we stopped before a blue plaque fixed to a handsome 18th-century flat, and I received yet another historic jolt. This was the home of Hans Sloane, prominent naturalist and physician who attended to Queen Anne and was a benefactor of the British Museum. So this, I finally learned, was the Hans Sloane of Sloane Square, Sloane Street, and the elegant Hans Place.

''Why was this door built so wide?'' Ann Murray asked, stopping before a splendid portal with brass handle and knockers opposite Bloomsbury Square. ''In the 18th century,'' she answered, ''ladies had huge skirts, high hats as well. They traveled about on sedan chairs which were carried through the door by two men. And why was the first floor (second floor to you Americans) called the drawing room? Because the ladies withdrew there after dinner.''

When we had strode up Museum Street and stood before the storied bulk of the British Museum, I was surprised to hear that Bloomsbury institution receive only a few lines. ''Robert Smirk built it in 35 years. He had the courtyard glassed over, and it became a famous reading room. It is the hottest place in London in the summer, the coldest in the winter.''

Moving right along, we paused just long enough to glimpse the house of George du Maurier, Punch cartoonist and grandfather of Daphne du Maurier; Bedford Square, Bloomsbury's grandest and most unspoiled tract of greenery; the Courtauld Institute of Artgalleries at Woburn Square, an unheralded trove of impressionist and post-impressionist paintings, and finally Gordon Square, home of Lytton Strachey, John Maynard Keynes, haunt of Virginia Woolf, Forster, George Bernard Shaw, and others of the Bloomsbury Group. Now the words of these eminent Edwardians began to flow, but I knew Ann Murray's time was getting short and my head was echoing with Poe, Pocahontas, and plane trees, so I promised the Bloomsbury Group a private visit on a slower day.