It was a week in the insular art auction world to rival the Wimbledon fortnight in tennis.

The two top auction houses, Christies of St. James and Sotheby's of Mayfair, staged a stirring sales competition with impressive collections of Impressionist and modern paintings that packed their ornate old salesrooms in London's West End to overflowing with dealers, collectors and interested observers.

As a steady parade of Picassos, Renoirs, Matisses, Monets, Toulouse-Lautrecs, Cezannes, Chagals and Modiglianis were knocked down from 11 in the morning until 10 at night, world auction records tumbled and millions of dollars in a half dozen currencies flashed by in brightly lit numbers on the salesrooms' incongruously modern computerized toteboards.

The more than 500 men and women at each of the auctions, many of them fancily dressed for what is also an important social occasion in the trade, competed with each other and with bidders telephoning from New York, Los Angeles, Zurich, Tokyo and Capetown, South Africa. "No dealer recognized in the field can afford to miss sales like this," said one art expert.

Christies led off on Monday with a rare group of 26 high-quality Impressionist and modern paintings collected between 1915 and 1929 by Swiss textile merchant Hans Mettler, who bought them on his travels to Paris. Because both he and his widow who died recently, seldom exhibited the paintings by Van Gogh, Cezanne, Bonnard, Utrillo, Renoir, Matisse and others, most of them had never been seen outside Switzerland before Christies put them on view for this auction.

The most sought-after painting in the Mettler collection, a ToulouseLautrec portrait of two women and a man in a box at the opera, "La Grande Loge," sold for a record $810,300 -- almost twice what any of his paintings had brought in an auction before. Artist records also were set by the $569.400 paid for a brightly colored pastel of flowers in a vase by Odilon Restel and the $646,000 paid for a landscape of a mountain lake by the Swiss modern painter, Ferdinand Hodler.

But Christies' finest hour came Tuesday morning when a huge, colorful portrait of a robust young sailor by Henri Matisse, part of an auction of mixed Impressionist and modern paintings, brought $1,560,000 from an anonymous American bidder -- more than double the previous auction record for a Matisse and the highest price ever paid at an auction for a 20th-century painting.

The Matisse price at Christies also was $10,000 higher than the record for an Impressionist painting, the $1,550,000 paid for Renoirs's "Le Pont des Arts, Paris," in an auction at Sotheby's New York salesroom in 1968. "But Matisse is not really an Impressionist," sniffed a Sotheby's spokesman, who said the Impressionist record still belonged to them.

Last night, it was Sotheby's turn when it auctioned off aother longheld collection of modern paintings from the family of Paul Rosenberg, the exclusive Parisian dealer at various times between 1913 and 1940 of Pablo Picasso, Georges Braque, Fernand Leger, Henri Matisse and Marie Laurencin. Rosenberg, who ran galleries in Paris and London, ,moved to New York just before World War 11.

More records were set, topped by the just over $1 million paid for a strikingly bright-colored Cubist still life by Picasso, "La Bouteille de Vin," which exceeded the previous auction record for a Picasso by more than $200,00. Artist record prices also were paid for a Leger and a Laurencin.

Sotheby's failed to set any more records in its final round of mixed Impressionist and modern painting auctions today, although there were gasps and scattered applause in the crowded salesroom when an anonymous French buyer successfully bid $320,000 for a delicate Renoir riverside landscape, "La Pecheur a la Ligne," of a man fishing and a woman reading the newspaper, that was dramatically close to the record Renoir price in 1968.

As experts expect at auctions of Impressionist and modern paintings for which prices are much more upredictable than for old masters, there were also big disappointments.

More than a quarter of the pantings Sotheby's put up for auction with the Ronoir, all by well-known and widely collected artists, were not sold because the bids were not considered high enough. And a large, heavily publicized Van Gogh in the Mettler collection, a golden landscape of a tree-lined avenue in Arles in the South of France, was kept by Christies when the bidding stopped far short of the $1 million expected for it.

"A fine picture of a very good date," Christies' Impressionist expert, John Lumley, said later about the panting, which Van Gogh made in Arles at the end of October 1888, just when Gauguin came to stay with him there. "But perhaps it's not the masterpiece people wanted."

Lumley said that "with the general price level so enormously high, it is not extraordinary that some lots go unsold." Other art experts said it also was not unusual for auction houses simply to place much too high a value on a painting, especially one that had not been on the market for 60 years. .

The Christies sale was "very successful" overall, according to the Lumley, and confirmed "the huge interest in Impressionist art."

Neither auction house wanted to discuss the obvious competition with the other, although experts at each closely watched the opposition's prices and enhusiastically touted their own records.

"Major sales in each field are scheduled together so that the dealers only have to come over once," said Sue Bond of Sotheby. Dealers at this week's auctions come from Britain, Europe, the United States and Japan, among other places. "These happen to be very exciting collections this week," Bond said.

Both Auctioneers -- Lumley of Christies and Sotheby's chairman, Peter Wilson -- conducted the bidding in a soft-spoken, genteel manner, from a raised chair, meeting the eyes of competing bidders to watch for subtle indications of their intentions.

Jumps in bids of from $1,000 to $50,000 at a time were signaled by a raised hand or finger, or a nod of the head. A gray-haired French woman in a modest print dress, who would not identify herself, outbid several rivals from the second row of gilt straightbacked chairs in the crowded Sotheby's salesroom today by almost imperceptibly nodding her head to jumps of $20,000 and $40,000 on the way to her succesful $1.3 million bid for the renoir.

That renoir was first bought in March 1885, for 18 francs by French publisher and collector Georges Charpentier at the auction the Impressionist painters organized themselves to raise money and gain recognition. It remained in the family until 1971, when British financier Nigel Broackes bought it at a Christies auction for just $1 million.

The bidding was more emotional for the blue and green like landscape by Ferdinand Hodler that sold at Christies Monday night for a record $646,000, four times more than any Hodler painting had realized at auction before. Hodler's work, recently given more international attention by retrospective exhibitions in the United States and Britain, is much sought after by the Swiss.

Three Swiss bidders, two in the Christies salesroom and one bidding by telephone from Zurich, pushed the painting's price up far beyond what anyone had expected. After one Swiss dealer dropped out at $360,000, another one standing at the back of the room jumped in at $555,000.

As the auctioneer relayed the bids back and forth between him and the bidder in Zurich through an assistant holding the telephone, the line suddenly went dead when it was up to the bidder in Zurich to top a bid of just over $600,000. The mounting tension in the hot salesroom broke as the rest of the dealers, sweating under the spotlights focused on the auctioneer and the paintings, laughed loudly.

Then, after the connection was restored, the winning bid was trasmitted from the telephone by the sales assistant. The dealer at the back of the room, who had been pausing longer and longer before finally nodding his head to the rapidly escalating bids, did not move this time, and the gavel fell.

"I have never seen a duel like that in an auction room," Lumley said afterwards. "it was fantastic and shows what the atmosphere can produce." CAPTION: Picture, Picasso's "La Bouteille de Vin," sold by Sotheby's for just over $1 million