It was the week that shook the art world -- and it is not over yet. Since 8 o'clock on Monday night pictures worth a total of $50 million have been placed upon the block in Manhattan's salesrooms, and the biggest plum of all -- the $5.2 million Vincent van Gogh landscape that Henry Ford II sold at Christie's Tuesday night -- is on its way to Washington.

Its anonymous new owner, who purchased it by telephone, has agreed to lend the picture to "Post-Impressionism: Crosscurrents in European and American Painting, 1880-1906," the summer exhibition that will open on May 25 at the National Gallery of Art.

Handsome as it is, "The Garden of the Poet, Arles" is now known around the world for another reason. Depending how you calculate, the picture Van Gogh painted for his friend Paul Gauguin is the most or second-most expensive picture ever sold at auction.

True, the $5.54 million Velazquez sold in 1970 was knocked down for more, but auctioneers in those days did not add, as they do now, a 10-percent buyer's commission to the hammer price. The buyer n the telephone actually paid $5.72 million for the Ford Van Gogh.

"Its label here will read, 'Lent Anonymously,'" said Carter Brown, the Gallery's director. "I don't know who bought it, I don't want to know. David Bathurst of Christie's knows. He arranged the loan." All Bathurst would say is that the new owner is not Greek shipping tycoon Stavros Niarhos, as has been widely rumored.

Brown is well aware that at museums, as at auctions, pictures with such price tags tend to pull in crowds. One reason that the audiences for "American Light," the Gallery's Luminist show, have surpassed expectations is the "The Icebergs' by Frederic Edwin Church, which holds the record for an American painting -- it sold last year for $2.5 million ($2.75 million if one includes the buyer's premium) -- is included in the show.

Many find it thrilling to watch an auctioneer, his voice calm, his eyes darting, sell a million-dollar object. "It is," says John Marion, president of Sotheby Parke Bernet, "the best free show in town."

On Monday night, while the numbers spun on the computerized currency converter installed above his head, Marion sold 40 pictures from the Garbisch collection for a total of $14.8 million. There were 1,200 people present. They were rich, and they looked it. With the money they had spent on their hand-made suits, their perfumes and their limousines, one could perhaps buy a second-rank Van Gogh. They were there to see, and to be seen. "With 40 objects sold," said Marion, "not all them were buyers."

The next night at Christie's, 1,000 people, comparably turned out, were jammed into four salesrooms while Bathurst sold 10 of Ford's fine paintings, one of them the Van Gogh, for a total of $18.3 million. That evening's two-part sale earned $25.5 million. The total the next night at Sotheby Parke Bernet raised the total for the three days to about $50 million.

"To tell the truth," said Bathurst, "we did not expect to take in quite so much."

"The reason," said Sotheby's Marion, "is that great works from great collections do command great prices. Cream rises to the top."

Marion announced yesterday that another auction, which may bring in even more than the Ford sale, will be held at Sotheby Parke Bernet next fall. Several of the pictures -- among them two Van Goghs, a Rembrandt, a Picasso that was once owned by Gertrude Stein, an early Cezanne, and a Degas portrait of Mary Cassatt -- are expected to sell for more than $1 million each. All come from the collection of the late Andre Meyer, the New York investment banker who died last fall.

Witnessing a well-dressed gentlemen hold up a wooden pencil -- a gesture meaning he has just offered to expend another $100,000 -- is, says Parke Bernet's Peggy Shannon, "a spectator sport."

John Rewald, the dean of scholars of Impressionist painting, says he can remember when the crowds were thin at New York auctions. "In those days," Rewald said, "they were thin at museum openings, too. That, of course, has changed. Openings, and auctions, are now social events."

"It's like going to the World Series," said Peggy Shannon. "Dealers and collectors from around the world come to check the market, to see and to be seen. A few of them even buy."

"Buyers," Bathurst said, "come from America, Europe, and Japan. There also are the odd few from South America or South Africa. The Arabs are nonstarters."

Some of them expect to make a handsome profit when eventually they sell the works that they have bought. One Money, "Argenteuil: Flowers by the River Bank," which fetched $570,000 at Sotheby Parke Bernet on Wednesday night, sold at the same auction house for $8,500 in 1952. In 28 years the picture increased in value by 7,000 percent, or about 250 percent a year.

"Buyers," said Washington's Ted Cooper, one of the dealers present, "do not always place a dollar figure on the enjoyment -- or the statue -- that they get from owning a first-rate work of art."

This week in New York, many of the buyers preferred anonymity. One of the Ford pictures, a portrait by Cezanne that fetched $3.9 million, went to the Kimbell Art Museum in Fort Worth. The others went to buyers whose names are not known.

"The Garden of the Poet, Arles' was included in the Royal Academy's Post-Impressionist exhibition, from which ours is derived," said Carter Brown. "Two other pictures owned by Ford -- another Van Gogh landscape and a Gauguin seascape -- were also in that show. I was in Kyoto when I heard that Henry Ford was about to sell his pictures. We spoke to Christie's then. We thought of going after the seascape by Gauguin -- but it has already left the country. It seems to me we're fortunate to be getting the Van Gogh."