Providential or coincidental? There's an R in Loire. The bivalve eating R months have returned. And, the white wines of the Loire have a well-recorded affinity with seafood of all kinds. Think of mussels and muscadet, scallops and sancerre, freshwater pike and pouilly-fume. They sound and taste just right for each other.

The Loire Valley is a ribbon of wine regions for the lower half of its 700-mile length, the ends producing dry whites and the center, the beautiful chateau country, producing fruitier styles. Judging by the selection available, we seem to prefer the dry whites to the chenin blancs of Vouray. So, this Loire journey starts with the eastern or upstream regions of Pouilly-sur-Loire and Sancerre.

They're quiet, unspoiled towns, on opposite banks of the river. Sancerre, sitting on top of a steep, vineyard-covered hill, is the prettier of the two, but there's not much to choose between the wines themselves. The better quality wines are made from the sauvignon blanc grape. Dry, flinty, occasionally earthy, they can be tart enough to be mouth-watering.

These pouillys are labeled pouilly-fume, to distinguish them from the lower quality wines of the region, which use the chasselas grape and are labeled pouilly-sur-loire. One theory is that the fumes are so named because they have a smoky, gun-flint smell. I prefer that of Patrick de Ladoucette of Chateau de Nozet, who said that the smoke refers to the morning mists that hang in that pocket of the valley.

Small vintages in 1977 and 1978 forced prices up to a level that is often not justified, Chateau de Nozet being the prime example. After all, fumes and sancerres are pleasant, fresh-tasting, but not particularly complex wines, to be drunk within three or four years. However, with salmon and scallops now costing over $6 a pound, the current prices of the wines are probably in proportion with their seafood partners.

The quality of the '79s is good and prices are steady. Of the fumes recently tasted, I liked those of Michel Redde, $8.99; Gaudry Denis, $9.95; and Chateau de la Roche, Guy Saget, $8.99.

The Redde has an earthy nose and a crisp taste. The Gaudry is mildly herbal on the nose and is very dry, and the Chateau de la Roche is smoother and richer than the other two. In sancerres, the '79 La Terre des Chasseignes, $8.99, has a herbal flavor and a good crisp finish.

Down to the sea, and the region surrounding the port city of Nantes. This is the region of the muscadet, the grape which matches the delicate Atlantic seafood, the best coming from Sevre-et-Maine, a department just south of Nantes.A muscadet is very dry, lightly scented, light-bodied, to be drunk young while it's still fresh.

Once it was useful to read on a label that a wine had been bottled "sur lie," meaning that it had never been racked off its lees, the deposits of fermentation. To bottle "sur lie" was to retain the delicate character of the muscadet. However, it is now murmured that many producers no longer bother, yet continue to print "sur lie" on the labels.

Sevre-et-Maine had good, if small, vintages in '78 and '79, and two particularly pleasant examples are '79 Chateau la Noe, $5.99, and '79 Gasais, $6.50. POST SIP

An all-round red from Portugal: 1968 Garrafeira, Caves Velhas, $5.99. Medium-bodied and smooth, it's a wine for meals, not medals, and is ready to drink now.