Folkestone -- by Orient Express

At first it didn't seem quite right: relaxing in an elegant armchair in an immaculate cream and brown Pullman car on the Orient Express with the memories of Graham Greene, Hercule Poirot, and King Carol of Romania - but not going to the Orient.

In fact, I ended up at the rather more prosaic destination of Folkestone, an English Channel port of seashells and subdued charm, hardly to be compared for romance or intrigue with Istanbul, Venice, or Milan.

Yet it was the Orient Express, or rather, a restored, modern English version of one of the four trains now running in Europe which include the evocative words ''Orient Express'' in their names.

This one offers not the usual sumptuous overnight trip across the channel to Gare Austerlitz in Paris and on to the canals of Venice, but day excursions into the English countryside instead.

Along with (among others) a British couple celebrating their wedding anniversary, two sisters-in-law from Mississippi, and splendidly brass-buttoned chief steward Brian Hannaford, I took a journey back into the nostalgic past in the manner the British do so well.

Surrounded by lace, crystal, highly polished ash-and-marquetry, pink lampshades on brass bases, snowy table linen, carpets, deferential waiters in primrose jackets, flowers, and the cleanest windows ever seen on British trains, we ate a light lunch of vegetable soup, cold roast chicken, salad, and black currant fool, during the hour-and-a-half run to the coast.

There we changed to a luxury bus to visit and have a handsome afternoon tea at Leeds Castle in Kent, said to be England's oldest medieval castle, a jewel surrounded by a moat, black swans, and daffodils, where Noel Coward once played, Richard Tauber sang, and kings and princes lived for 300 years.

Not a film star, a Rothschild, or a Mata Hari in sight all day - although Brian Hannaford, in resplendent chocolate-brown coat and black bow tie, did lead us through the carriages, recalling the days he served on the deluxe prewar Kings Cross-to-Scotland run, and reckoning that recession or no recession, there are always people ready to pay extra for ultra-high quality.

''The lamps are not screwed into the window ledges on this train,'' he said with satisfaction as we walked through cars named (no vulgar numbers here) Perseus and Cygnus, Minerva and Audrey.

''And look at these,'' indicating a restroom with mosaic floors, marble handbasins, and stained-glass windows. ''Three thousand pounds to restore each bathroom alone. . . .''

Audrey was built in 1932 for the Brighton Belle and twice carried the Queen. My own car was Perseus, previously used, I was glad to note, by royalty and heads of state.

All the old, narrow-gauged cars have been meticulously restored to modern safety standards by craftsmen at Carnforth in Lancashire. Inside, all is as it was in the heydays of train travel. We sat on free-standing armchairs with floral designs and antimacassars at individual tables. A conductor welcomed us. When we stopped for a few minutes, he was back with an explanation.

Some of the waiters worked on the old Pullman trains: The couple on their anniversary recognized one from the Brighton Belle.

Total cost of the restoration of the entire London-Venice line: (STR)12 million (about $18.4 million).

The day trips are possible because the British part of the train does not cross the channel into France.

It glides from Victoria to Folkestone at 11:44 a.m. every Friday, Sunday, and Tuesday, starting April 1, taking passengers through the green Kent countryside to a Sealink ferry and the 90-minute crossing to Boulogne, France.

There, restored gold-and-blue sleeping cars of the original Compagnie Internationale des Wagons Lits et des Grandes Express Europeens convey onward passengers through the night in rosewood and armchair luxury, reaching Paris at 10 past 10. The 12-mile Simplon tunnel from Switzerland to Italy comes early the next morning, Milan at 9:15 a.m. and Venice at 12:52.

On Sundays, Tuesdays, and Thursdays the British train picks up returning travelers in the late afternoon and whisks them up to Victoria Station in an hour and a half.

To take advantage of the schedule, the private company operating the train (officially called the Venice-Simplon-Orient-Express) began offering day trips last autumn.

About 2,500 people visited Leeds Castle or Eastwell Manor, both in Kent. This year the company offers Leeds Castle on Thursdays (train and lunch south, bus back); the tiny 13th-century Hever Castle (home of Anne Boleyn) on Fridays (bus down, train and afternoon tea back); and Beaulieu (pronounced by the British as ''Bewley'') from Waterloo Station on Saturdays, with its national motor museum, palace house, and abbey ruins.

Officials hope for many more visitors, particularly Americans. Company spokesman Tony Spalding estimates that 30 percent of the 20,000 people who rode the train last year were American. He hopes that a total of 40,000 passengers will appear this year, and that 35 percent will be from the United States.

The day trips to Leeds Castle and Hever Castle cost (STR)70 per head ($107), with lunch on the train, tea at the castle, and the bus all included. Beaulieu costs (STR)90 ($137) because you travel there and back, and have lunch and tea, on the train.

''Yes, it's expensive,'' said Betty Early of West Point, Miss., who had read about it in a British travel magazine. ''But it is worth it - for the elegance, the beauty, and the superb service.''

Virginia Van Cleve of Indianola, Miss., nodded. In England for 10 days, she and her sister-in-law had seen Blenheim Palace, the Cotswolds, the National Gallery, and an architecture museum in London, and had been delighted at the musical ''Cats'' and at Rex Harrison in Shaw's ''Heartbreak House.'' But the Orient Express was special.

One way from Victoria Station to Folkestone is (STR)30 ($46) per person, with lunch included. The whole journey to Venice is (STR)295 ($450) one way - and you have to buy your own dinner in France. ''We key our prices to the first-class air fare - and offer accommodations as well,'' said Tony Spalding.

My favorite moments of the day included glimpses of green Kentish fields and white Kentish sheep through crystal-clear windows as waiters hovered skillfully with lunch. . . . The quiet pleasure in it all of the sisters-in-law from Mississippi. . . . The man on his anniversary who kept the secret of the trip from his wife for six weeks and thinks he has sold four Orient Express tickets to friends on his daily commuter train. . . . The serenity and the comfort of the oak rafters, the mullioned windows and the fairy-tale setting of Leeds Castle set in 400 acres of parkland.

Until 1976 the castle was owned by the late Lady Baillie, whose mother was a member of the Whitney family of New York. She worked on its restoration for 50 years. A Mideast foreign ministers' conference was once held there because of its secluded setting.

For more information about the Orient Express day excursions, write to Venice Simplon-Orient-Express Inc., One World Trade Center, Suite 2847, New York, N.Y. 10048, or call (212) 938-6830. There are two reservation numbers: in New York at (212) 661-4540; outside New York, 800-223-1588.