It's no secret that there has always been strong rivalry among the French Rothschilds, but it recently reached a peak.

Baron Edmond de Rothschild made his debut in the Bordeaux with country by giving the Fete de la Fleur (a yearly event celebrating the flowering of the vine) on the grounds of his newly acquired Chateau Clarke.

Now, the situation was thick enough as it was, between the Chateau Lafite Rothschild (a grand-cru classe that belongs to the banking branch of the family) and Mouton-Rothschild (long second-cru classe until 1973 when it made it to grand-cru level) belonging to Baron Philippe, without having still a third Rothschild buying into that region.

What made it worse is that Baron Edmond (who owns one-sixth of Chateau-Lafite) bought Chateau Clarke in 1973 without consulting in Lafite cousins and that he plans to develop, run and sell his wines without consulting them either. His main adviser is Baron Francois de Gunzberg, a well established wine marketing consultant and owner of Chateau Greysac.

Why would Baron Edmond do such a thing? According to some, he got tired of having no say at Lafite and decided to have his own vineyard for his son, Benjamin, to show that he too, could. Other people, notably a French marquis, claim that it is a way for Edmond to get access to Bordeaux winery nobility of sorts, adding, "Remember, the Rothschilds are not admitted into the Jockey Club."

Nonsense, according to others: If Edmond were that kind of a social climber, he would have bought Chateau Margaux (grand cru classe) which was offered to him before it was sold to Andre Mentzopoulos.

Chateau Clarke is only a cru bourgeois and needs complete re-doing. Edmond has already spent between $4 million and $5 million to put in a new wine cellar and vinification plant. To the original 15 acres, he is also adding 177 more acres of vines.

The more likely hypothesis is that Edmond, reportedly the richest of the Rothschilds (which does not help), is constantly investing in new ventures, with a preference for leisure and consumer's goods. Recently he added to Chateau Clarke the controlling interest of Savour Club, a mail-order wine firm. He is also considering buying into California vineyards.

The funniest line on the subject came from Jean Cordier, who said he did not know anything about all that new gossip nor did he care because he was not from Bordeaux anyhow. "I'm from Lorraine," he said, shrugging, "and my mother is an American." Which made it all the more piquant because Cordier, with seven Chateau, is reputedly the biggest dealer in Bordeaux region (with 22 million bottles a year, a large part of which is exported to the United States).

In any case, the Lafite cousins are mad at Edmond for wanting to run his own show. "Why," said Baron Elie, who until recently was Lafite's manager, "It's right down ungrateful of him to act the way he does, considering the kind of dividends he collects from Lafite. the least he could have done was to come to us for distribution."

And to show him, the Lafite cousins did not come to the party, nor did they open the chateau for Edmond and his guests. But all that backbiting did not faze Edmond much nor did it spoil his party. The combination of his financial resources and his wife, Nadine's friendliness did wonders.

Instead of the traditional - and, many said, boring - luncheon they had a dinner-dance for 650 people under a huge tent, lit by giant crystal and dimmer-controlled chandeliers. The orchestra had been flown in from Geneva, special guests, including Eve Barre, the wife of the French premier, had been brought over by private planes and the food came from the best caterer in Bordeaux.

But the real miracle of the evening was the wine list which included nothing but grands crus classes and all five of them: Mouton-Rothschild, Haut Brion '70, Margaux '67, Latour '64, and Lafite-Rothschild '62. And that, even in Bordeaux country, is pretty intoxicating.

The guests included practically all chateau owners of the region and guests who also happened to be customers. Besides Mme. Barre, Baron Edmond, who wanted to give the function a European flavor, invited Luxembourg's premier, Gaston Thorn, and his wife, Lillians, and from Belgium Prince Antoine de Ligne.

The nice quiet American who was there not saying much but tasting plenty was Michael Stone, who recently sold his vineyards to Coca-Cola and may join Baron Edmond in his California venture. Other bigwigs included French politician Aymar Achille Fould (who owns the Beychevelles Chateau nearby), Sir Hugh Astor, former president of The Times of London and American wine expert Alexis Lichine.

Baron Philippe, for Mouton-rothschild, and his daughter Philippine (a comedienne in real life and a real pistol on and off-stage) were there too and tried to give the weekend a kind, family flavors by throwing a luncheon party the next day at their chateau. The baron, who inherited it from his grandfather in 1924, "when it was nothing but a building with a pile of manure," has spent a lifetime fixing it up with his late wife American-born Pauline.

The result, including a unique wine museum, was extraordinary enough but that would be without counting the baron's private cellar of 100,000 bottles "which I know one by one," said the maitre des chaix, Raoul Blondin, 67, who was born on the property. Answered Mrs. Barre: "I think it's you who should be prime minister." CAPTION: Picture, Baron Edmond Rothschild with Eve Barre; by Hebe Dorsey