THE ALL-NEW GLACIER EXPRESS

AS our gleaming red and white train slid into the black interior of the mountain beneath the Furka Pass, our guide announced ''You are the first people to pass through the Furka Tunnel - the world's longest narrow gauge tunnel.''

Between Zermatt and St. Moritz, from the French Valais to the Italian Ticino to the south and east, there is at last a year-round link.

Our group felt rather foolish as we eagerly embraced our moment in history. We shouted and cheered and jostled each other for photos. And knew this was probably the best we'd do. No breakthroughs in silicon chips or the secrets of the universe for us. Just a ride on a red and white train.

But the moment was historic nonetheless. We quipped about ''light at the end of the tunnel'' and murmured only half-in-jest hopes that the ''shot-crete'' lining the tunnel would hold as if it were really rock. But we also did homage to the nine years and 340 million Swiss francs it took to tunnel through 20 kilometers of mountain.

Between 1801 and 1805 engineers under Napoleon carved a road over the Simplon Pass west of the Furka, facilitating the movement of troops from France into Italy. By the end of the 19th century even the St. Gotthard Massif in the very heart of the Alps - and just east of the Furka Pass - had been penetrated by both rail and road.

The Furka, too - so precipitous that its slopes drop away like the sides of a saddle - had been stamped with a road since the 1860s, but a lot of good it did when the winter's snows came. The St. Gotthard and Simplon passes by the 1980s were tunneled for cars, making travel almost always possible on these north-south routes. But the old Furka road would still shut down from November to early June - as did the railway which was established in 1926 - and skiers and sightseers alike would find themselves detouring north to Zurich and back down again in an awkward and time-consuming attempt to go west and east.

The Swiss, by way of celebrating the opening of the Furka Tunnel - a triumph over nature - are inaugurating a ''new'' Glacier Express train trip from Zermatt to St. Moritz. Since 1928, there has been a train called the Glacier Express, which took a scenic route through the Furka-Gletsch area, but ground to a halt when the first snows came round. With the Furka Tunnel now enabling trains to skirt risky avalanche areas, this inconvenience is a thing of the past.

The ''new'' Glacier Express, a joint project of the Furka-Oberalp, Brig-Visp-Zermatt, and Rhaetische private railways, will run year-round through 150 miles of Alpine splendor. At 7 1/2 hours from Zermatt to St. Moritz, it's easily the world's slowest express.

Our group boarded our red and white chariot in Brig, in Roman times an important staging point north of the Simplon Pass. Today, Brig is a junction for principal roads traversing Alpine passes and the linking point for the spur train from Zermatt on the Glacier Express.

Our entrance into Brig marked more than the beginning of a historic journey. We had come from Lausanne, where we were delighted by baroque elegance, by French pastries and language, and by the predictable charm of sailboats moored in the sheltered harbor at Lausanne-Ouchy.

We enjoyed a last touch of southern influence as we watched for roadside poplars planted by Napoleon's cohorts between Martigny and Sion, and thought wistfully of the apricots, peaches, and strawberries which, we were told, thrived in the valley's almost Mediterranean climate.

No wonder Brig jarred us into a state of alert, as the Upper Valais became Oberwallis, the language no longer subtle French but angular German.

Neither the serpentine embellishments of Lausanne's Beau-Rivage Hotel nor the ornate sculptures of Lausanne's Gothic cathedral exist in tiny Brig. Its main landmark - the Stockalperschloss, a 17th-century palace of a merchant prince - is an engaging mishmash of plain towers topped with great bulbous domes and galleries lined with tiers of graceful arcades.

As we left Brig on our way to the Furka tunnel, the invigorating presence of blue, cloud-scattered sky gave way to a gloomier gray. No problem, I thought, as we neared the village of Fiesch, 18 miles to the east of Brig. We passed tiny Morel, whose cableways climb to the threshold of the Aletsch Glacier, the largest glacier in all of Europe - 66 square miles of snow and ice.

Although we were by now a long way from Lake Geneva, we were still traveling parallel to the Rhone River. Now we were near its icy source, the terminal cataract of the immense Rhone Glacier. From this point, we were finished with the Rhone. Its way was west, back toward Brig as it is gradually transformed from a tumultuous mountain stream to a more tranquil waterway.

At last we were in Oberwald, our brief stopping point before entering the Furka Tunnel. Beyond the tunnel, we would find we had traversed more than a mountain pass. Ahead lay new territories of thought and speech. Except for an hour's stop in Andermatt - crossroads of the Alps turned ski resort - our journey now was straight ahead to Chur.

The market town of Disentis, beyond Andermatt, is the spiritual heart of the Grisons, a largely rural canton where the official language is Romansh - a dialect surviving from the days when the conquering Romans blended their folk Latin with the local talk.

As we entered Chur, we were finished with the Glacier Express. Our tallies of bridges (291) and tunnels (91) were at last laid to rest. We felt like armchair pioneers - the hard work for others, the accomplishments ours to admire. Practical details:

Travel agents sell Glacier Express package tours, as does the Swiss National Tourist Office. Your rail ticket enables you to buy five half-fare tickets on such excursions as the Castle of Chillon, Gornergrat by cog railway, and a half-day tour of Geneva's countryside.