FEDERICO Paternina has what may be the world's largest wine-aging room under one roof. In a modern hangar-like structure blanketing 2 1/2 acres, in Spain's Rioja district, 35,000 225-liter casks of Paternina's Blue Band wine are stacked five high. That is more than 10 million bottles.

The largest exporter of Spanish wine to the United States, Paternina was bought 10 years ago by a conglomerate, Rumasa, the largest corporation in Spain, with substantial holdings in everything from banks to hotels to manufacturing. Soon after it bought Paternina, the corporation rebuilt the 52-year-old buildings; the resulting facility is extraordinary. All the wines can be moved between areas through an elaborate system of color-coded pipes in a system directed and monitored at a large console.

Wine making in Rioja -- which represents but 5 percent of the country's total production, yet dominates the export market to the U. S. -- is an industry over 1,000 years old. The traditional face of Rioja also can be seen at Paternina. In Ollauri, a town a few miles from Haro, the westernmost town of the region, are the firm's "old" cellars, carved out of rock by Portuguese and Galician farmhands a century or two ago during the winter months when there was no work in the fields. Thick layers of black, and sometimes yellow and red, mold envelop the surfaces of the damp and chilly vaults. One and one-half million bottles, many so encrusted they form part of the walls, fill racks. The oldest wines date back to 1904.

Many of the 42 wineries in this narrow, 80-mile-long band of northeast Spain are small -- for example, highly regarded Marque's de Riscal and Marque's de Murrieta. However, some, like Bilbainas, are substantial wine-producing corporations, in many cases with top management located in modern Bilbao, 50 miles to the north on the Atlantic coast.

Spain, including Rioja, is a land of traditions, and traditions, both good and bad, die hard. To start with the good, there is continuity. Most of the grape growers, who frequently grow other crops as well, have been producing grapes for generations, even centuries. Similarly, winery employes have been wedded to the companies. In Haro, the resident manager of Bodegas Bilbainas, one of Rioja's largest and best producers, has been with the company 42 years; his father retired after 64 years there.

Tradition affects wine making and wine attitudes, too. One tradition has been that a good white is an old white. A highly regarded restaurant in Burgos, just west of Rioja, listed a number of white wines. The most expensive by far was the oldest, a 1962 white rioja, which sold for the steep price of $22. Some young whites listed for $4 and less. Happily, the trend is moving away from veneration of old whites. As for the reds, there has been a tendency to age the wines long in wood. But while the leading producers are making strides to bottle their reds with no more than two to four years of barrel aging, Bilbainas bottled its 1970 Vi'na Pomal Reserva, the top of its line, this past fall.

Wine makers in Rioja believe that their future, at least with sophisticated export markets, lies in red wines, even though Rioja produces about as much white as red and a considerable amount of rose', too (reliable statistics are very difficult to come by). Furthermore, at a busy restaurant in Haro every diner was drinking red wine, regardless of the food consumed.

For those contemplating a visit to Rioja, there is simple advice: Learn Spanish. Rioja is not Napa, and finding someone at a winery who speaks English or even French can be an unrewarding effort. The people are friendly but generally do not realize that visitors want to taste the various wines. One winery offers some of its sparkling wine after a full tour. Paternina's chief of public relations speaks English, but the cellar master at Ollouri, Paternina Lopez, doesn't. It can be a frustrating, albeit exhilarating, experience to follow him silently around the old cellar. The frustration can turn to anguish when Lopez roguishly points to pictures on the wall of the Ollouri tasting room of himself, Ernest Hemingway and legendary bullfighters. The questions one could ask!

In addition to some of the best, Rioja wineries also make a substantial amount of poor wine.

The larger Rioja producers bottle a number of red and white wines under different names and in oddly shaped bottles. The names and bottle shapes reflect variations in quality and style, including the proportion of grape varieties and aging. Red wine in burgundy-shaped bottles is likely to be more full bodied than wine in bordeaux-shaped bottles. As a general rule "reserva," "gran reserva" and "reserva especial" appear on the longest-aged and best wines.

While Rioja is beset by high interest rates and inflation like the rest of the world, it manages to withhold its best wines from the market for a long time. Some wineries are just releasing their 1970 and 1971 "gran reservas."

Riojas provide the opportunity to acquire wine with some age at a reasonable price here. Many District stores have 10-year-old wines at around $8 a bottle or less, with Woodley Liquors, 3423 Connecticut Ave. NW, and A & A, 1909 Pennsylvania Ave. NW, having perhaps the best selections of mature wine. Each has several samples of the 1970 vintage and one of the 1964, both highly regarded in Rioja.

Unfortunately, there is virtually no chance to taste any of Rioja's oldest wines in the United States, although the 1977 Heublein auction did include two cases of red riojas: a case of 1924 Marque's de Murrietta brought $165, while a case of 1926 Marque's de Riscal brought $185.The next time a 50-year-old rioja is put on the block, the price may be higher.