Pleasant surprises await the traveler who explores the crossroads country of BELGIUM

VARIOUS reactions greeted us when we told people our summer vacation was to be exclusively in Belgium. There were snorts of disbelief: Who wants to go to Belgium? There were signs of vague indifference, as though this small country, wedged between Holland, West Germany, and France, could hardly be counted as a country in its own right. Mostly there were the ``I-went-through-Belgium-on-a-bus-once'' responses -- suggesting that an actual stop in Belgium would simply be good time wasted, when the glories of France and southern Europe were beckoning. Driving rapidly through at night, in fact, was the only way I had previously visited this maligned nation. Surely the land of Bruegel and Rubens had more to offer the tourist than roads to somewhere else.

It has.

In 10 days we scarcely scratched its surface. But what we did see convinced us that Belgium deserves to be on many more itineraries of Europe.

We discovered that Belgians are remarkably welcoming to foreign visitors. The capital, Brussels, headquarters of the European Community and of NATO, is, of course, permanent host to a large population of non-Belgians -- Eurocrats and businessmen, lawyers and military personnel -- yet its identity as a tourist attraction is not swamped by this lively cosmopolitanism.

Its famous main square, the Grand' Place, is a marvelous four-sided stage set of richly decorative architecture. It is medieval with baroque overtones, because much of it had to be rebuilt at the end of the 17th century, after a battering by Louis XIV's troops.

But instead of being overwhelming and impersonal, it is human in scale, accessible, and enjoyable. Combining a public generosity of spirit with a sense of amiable intimacy, this astonishing square (which you enter by narrow side streets that somehow vanish once you are in it) is a symbol of virtually everything we look back on with particular relish in Belgium.

Take, for instance, the new Museum of Modern Art in Brussels, situated in one of the fine, white classical buildings of the Place Royale, high up, overlooking the city. The display of modern works inside is extensive but also somehow exclusive, even secretive. Perhaps this is achieved by the unusual design of the museum. Instead of going up, it goes down. The visitor descends eight stories into the hillside.

Or take the day we spent lazing about in the Soignes Forest. This gigantic public park, wooded and grassy, stretches for 12,000 acres south of Brussels, all the way to Waterloo. (We later visited that battle site, of course.) In the forest we found a lake with fountains and little paddle boats, a tiny ferry platform offering transportation to an island-restaurant, and sun-drenched green banks.

A vacation can't be all sightseeing. This park was ideal for a no-pressure break -- and we felt simultaneously away from it all and part of the local scene. Relaxing Belgians strolled past us with their dogs, or jogged, or played games, or, like us, simply lounged around and chatted and gazed through the oak trees at the sky.

Or take our day in the historic city of Bruges. If you encounter other foreign tourists in Belgium, it is likely to be in this popular city, still so medieval in feel. But it is a place that invites sharing. And, anyway, there's no wonder it is so popular.

This ``Venice of the North,'' which reached the zenith of its commercial success in the 13th century and was in decline by the end of the 15th, is beautifully protected today. Hundreds of picturesque bridges span the canals. There are well-organized boat trips readily available. There are horse-drawn carriages. The glorious 13th-century Belfry Tower can be climbed for a splendid view over Bruges's conglomeration of stepped gables and pitched roofs and subtly textured brickwork -- or just admired from below. Two main squares vie with each other in this town, evidence of complicated rivalries in the Middle Ages, adding to the interest for today's traveler.

An art lover is likely to discover that seeing great paintings is alone a sufficient reason to vacation in Belgium. In the Groeninge Museum at least one supreme painting is a must: Van Eyck's `Madonna with Canon van der Paele,'' a masterpiece of so-called Flemish ``primitivism.'' Like the city it belongs to, this meticulous painting evokes a period of amazing cultural riches and sensibility. It is both a public manifestation of piety and evidence of a highly personal dignity. Again there is that mingling of the outward and the inward.

In Antwerp it was the house of that exuberant baroque painter Peter Paul Rubens which once again caught this feeling of the extrovert and the introvert. Carefully restored, the partly monumental and partly intimate house provides an impressive glimpse of the way one of the celebrities of the 17th century accommodated both his family and his work, his domestic and his exhibitionist sides. The grandiosity of this house never makes it impossible to believe that it also made an excellent and comfortable home.

In the Ardennes region of southern Belgium we stayed overnight in the attractive holiday town of Durbuy. Here was, by far, the most pleasant of the hotels in which we stayed, Le Sanglier des Ardennes. Old-fashioned and countrified, our small room overlooked the shallow River Ourthe, backed by tree-smothered cliffs, flitted over by hundreds of martins, and canoed by canoeists who, rather enchantingly, kept getting stuck downstream in sandy shallows and had to disembark in mid-river and walk.

Here, also, we had one of the two memorable meals of the vacation -- and in Belgium a memorable dinner scales the heights of gastronomic experience. The trout in a nettle sauce at Le Sanglier's restaurant was a work of art, mellifluously gentle on the palate. Both here and in the other exceptional restaurant we visited -- the world-famous Maison du Cygne in the Grand' Place in Brussels -- that delectable dessert, the bavaroise (Bavarian cream), was on the menu. And each of these houses offered its own variation on that sweet theme. The Maison du Cygne certainly expects its clientele to dress classily -- but the sacrifice is worth it. In Durbuy, dinner cost more than the hotel room, which gives a hint of Belgian priorities.

What other reasons are there for a tour of Belgium? In the summer there are markets and festivals, processions, carnivals, cavalcades, and folk dances.

And there are many other areas we'd like to see more of. We didn't, for example, see enough of the Ardennes, the hillier part of this generally flat country. We were not long enough, perhaps, in Antwerp to come to terms with this complex Flemish city. It would also have been fun to go inside the extraordinary ``Atomium,'' the theme-structure of the 1958 Brussels World's Fair, instead of having time only to photograph the outside. I would like to have visited Tournay, with its Romanesque cathedral.

In each city we did visit, the tourist facilities were excellent -- assistance and literature centrally available. In the north there are fine beaches. We enjoyed a visit to Ostend, with its long rows of bathing huts, fine sand, and colorful melee of striped windbreaks. We stayed in the vast, colonnaded Hotel Thermae Palace, which retains the atmosphere of an Agatha Christie 1930s hotel.

There are always surprising encounters with Belgium's medieval past. The row of guild houses on the Graslei River at Ghent stood out for us (and not just because we sat on the quay side and ate strawberries), and an unplanned arrival in the market square at Veurne provided a delightful surprise.

Then there's that unsurpassed national achievement, Belgian chocolates. Maybe you can buy them at home, but without doubt the right place to bite into these chocolates filled with fresh cream is in the middle of the Grand' Place right in the center of old Brussels. Practical information

For more information contact a travel agent or the Belgian National Tourist Office, 745 Fifth Avenue, New York, N.Y. 10022; (212) 758-8130.