Berries, berries everywhere in Finnish summer

''You know it's summer in Finland when everyone walking along the streets is eating strawberries,'' observed our tour guide. Knowing that this land of many lakes and streams has a fine reputation for producing some of the world's most luscious berries, we lost no time learning where they were being sold.

And so, as soon as our city tour was over, we headed for Helsinki's Market Square at South Harbor. There we found a colorful, bustling market beneath the massive ships that line the harbor.

Getting closer, we saw, under bright orange umbrellas, stall after stall filled to overflowing with mounds of glistening red strawberries. Each stall was doing a brisk trade, but the mounds never seemed to diminish as eager customers walked away with paper cones filled to the brim with berries.

When we bit into our strawberries, we found them among the sweetest and most flavorful we had ever tasted. Now we could understand why the extremely long days of intense light here mean so much to the berry season.

But this was just the beginning of our berry adventures in Finland as we traveled west of Helsinki to the historic city of Turku and north of the capital to attend the annual opera festival in Savonlinna.

I tasted my first Arctic cloudberries in a pudding served at Hvittrask, in the restaurant of a museum complex, the former home and studio of Finland's famous architectural trio, Saarinen, Gesellius, and Lindgren.

The flavor of cloudberries - which look something like raspberries except that the bumps are larger and are yellow - is difficult to describe, but it is perhaps close to the taste of a slightly underripe apricot.

Typical of many Finnish berry puddings, this one was thickened with potato starch, giving it a Jell-O-like texture. We discovered similar puddings, made of many different types of berries, all over Finland.

In Savonlinna, we had a dessert that rivaled the magnificent production of ''Don Carlos'' we later saw. It was a feather-light mocha torte made by filling layers of mocha sponge with whipped cream and a thin gloss of Arctic brambleberry preserves.

The brambleberry looks something like a raspberry, but it has a tart edge that added an exciting dimension to this Eastern-European-style cake.

But the Finns don't save their berries only for dessert. Back in Helsinki at a stunning restaurant called Valhalla, built in an 18th-century fortress and accessible only by water, we sampled our first reindeer.

To begin, we had a peppery, rich reindeer pate served with an indescribable but delicious ashberry jelly. Later in the meal, we enjoyed a gamy reindeer ragout served with a thin, sweet sauce of whole, tiny lingonberries - the latter slightly tart and reminiscent of cranberry.

What else do the Finns do with their berries? For breakfast, they might stir fresh blueberries into barley porridge. For a thirst-quencher, they make tall drinks of sweetened cranberry juice.

For a salad, they toss shredded red cabbage with black currants. And for cold soups, they stew blueberries, gooseberries, or raspberries in water, adding potato starch to thicken and to give the soups their characteristic sheen.

Here are two unusual Finnish recipes using berries.

This very easy and delicious recipe is taken from ''The Finnish Cookbook,'' by Beatrice Ojakangas (Crown, $7.95), out of print but being reissued by the end of the year. Blueberry-Strawberry Pudding 2 cups sliced strawberries 1 1/2 to 3 tablespoons sugar 2 tablespoons potato starch 2 cups picked-over, cleaned blueberries 1 cup heavy cream, whipped (optional)

Combine strawberries and 1 1/2 cups water in saucepan. Bring to boil, cover, and simmer until slices turn very pale and have rendered juice, about 10 minutes. Drain pressing pulp with a spoon. Add sugar to taste.

Place strawberry juice in the saucepan. Dissolve the potato starch in 1/2 cup water and whisk into berry juice slowly, over medium heat. Simmer, whisking frequently, until mixture thickens, about 10 minutes. Adjust sweetness, remembering pudding will taste less sweet when chilled.

In a heatproof serving bowl pour hot pudding over blueberries. Cool to room temperature and then chill before serving. Garnish with whipped cream. Finnish Raspberry Rice 1 cup cooked, fluffy rice, unsalted, chilled Dash salt 1 cup heavy cream 1/4 cup sugar 2 cups fresh raspberries

Add salt to rice. Whip cream until stiff and add sugar to it. Fold whipped cream into rice, adjust for sweetness, and turn into a serving dish. Top with raspberries and serve. Serves 4.