Today, the croissant has become one of the hottest new consumer items in the century of the common man, putting some joie de vivre in the staff of life. At Sara Lee, croissants have now outstripped pound cake in sales volume, freezing smiles on the faces of competitors. At Roy Rogers, the name of the product has been Anglicized or westernized to ''crescent rolls''; soon there will be little difference in the American pronunciation of croissant and crescent. The rise of the croissant has taken place in the midst of the explosive popularization of the bagel. This eastern European round roll was traced by folklorist Leo Rosten to 1610 in Cracow, Poland, where indigent Jews who lived on black bread would treat as a delicacy the roll made with white flour, simmered in boiling water, then baked and glazed with egg white. As this culinary delight traveled to Germany, it was called beugel or beuglich, dialect words for ''ring-shaped pastry,'' perhaps from beugen. ''to bend.'' Only a generation ago, its production and consumption was generally limited to cities with Jewish populations. Today the bagel has broken its ethnic mold. From Whatsa Bagel in Chevy Chase, Md., to the Bagel Chateau on Third Avenue in New York, to Bims in Safeway Supermarkets across the country, the marketers of the chewy roll are reaching for an all- American clientele. Bagels are big business. Of course, a clash was inevitable. People whose mouths water at the fragrant flakiness of a croissant turn up their noses at the roundly resistant bagel. For their part, bagel mavens, who have their mouths fixed for the crisp coating and toothsome toughness of the bagel, poke their forks suspiciously at what seems to them to be a greasy, tasteless Danish. Psychologists understand the inherent antipathy between the croissanteur and the bagel maven. The shape of the croissant is that of the new moon, symbolizing openness to change and receptivity to ideas, while the spheroid bagel offers the symbol of the closed circle, complete it itself, perfect as an egg, asserting its traditionality. As a result, people who like bagels distrust people who like croissants. A bagel is for tearing apart with a satisfying display of strength, or slicing dangerously with a sharp knife; a croissant is for gently pulling apart. For their part, people who like croissants look askance at the bagel crowd: A croissant is light, flaky, accommodationist, digestible. A bagel lies in the stomach like a circular lump of lead.
