Buoyed by lowered expectations, an intimate collection of mostly modest works of art by mostly major masters sold for a total of $6.8 million last night at Sotheby Parke Bernet, the Manhattan auctioneers. Sotheby's had placed a value "in the vicinity of $8 million" on the 73 objects sold by Leigh B. Block, the Chicago industrialist -- but compared to the disastrous auction totals of the last two days, it was regarded as a triumph by Sotheby's auctioneers.

Last night's results were about what Sotheby's had expected. There were no million-dollar objects for sale and some results were disappointing, but Sotheby's officials felt that they had won a significant victory over Christie's, their chief New York competitor. "The two-day depressions is over," said John L. Marion, Sotheby's president and chief auctioneer. He was referring to the six far less successful sales organized by Christie's earlier in the week.

In one Christie's sale of German Expressionist pictures, two-thirds of the objects offered had failed to find buyers. In other Christie's auctions, works by Picasso, van Gogh, Renoir, and Rene Magritte also went unsold, in part because the minimum purchase prices set by the auctioneers turned out to be too high.

"We do things differently here," said David Nash, Sotheby's director of fine arts sales. "We have more realistic minimum prices. We set more realistic estimates." The Block prices were not all that high. Only three of the 73 pictures failed to reach the minimum price set by their consignor -- a Degas, a Boucher and a Jan Brueghel.

"Mr. Block is very happy," said Nash. "He says we run a good shop."

In these days of high inflation, costly cash and a strong dollar, million-dollar pictures are not easily disposed of, but the pictures Block offered for sale were for much less than that. The collection that he and his late wife had formed was rich with relatively affordable objects by such masters as Picasso, Toulouse Lautrec, Georges Braque, Monet and Manet. The record Monet price is $1.4 million. The Block Monet sold for $170,000. The Gauguin record set last year at Christie's is $2.9 million. Block's Gauguin -- the most expensive object sold last night -- went for $570,000. The Picasso record, set at Sotheby's last year, is $3 million. A 1943 Picasso still life, an oil nearly five feet high, last night fetched only $210,000. A Degas portrait had sold the night before for $2.2 million, but Block's Degas went unsold when bidding only reached $230,000.

Seven auction records were set last night: Honore Daumier's "Outside the Print-Sellers Shop" went for $420,000 to a New York dealer. A Giacometti sculputure brought $360,000. A Guardi view of Venice painted in 1758 went for $320,000. Record were also set for sculpters by Alexander Calder ($19,000) and Jacques Lipchitz ($75,000), and new highs were achieved for a 1978 painting by California's Wayne Thiebaud ($37,500), and 1953 canvas by England's Ben Nicholson ($220,000) and for a drawing by G. D. Tiepeolo ($77,500).

Ten Flower watercolors by Piet Mondrian, far better known for his rigorous rectangular abstractions, sold for a total of $413,500, more than a hundred thousand dollars above the presale estimates. Though bidding was spirited, one buyer won them all.

"Christie's estimates were much too high, especially for European dealers," said one of them, Hanbs Redies of Dusseldorf. "In former times I bought a lot in New York. But the value of the mark, via a vis the dollar, has fallen 25 percent since October. For a dealer, that 25 percent is the difference between the buying and selling price."

Block's late wife, the daughter of advertising magnate Albert Lasker, had hung most of these small pictures in her Chicago home. Four of the best objects in the collection -- pictures by Klee, Degas, Seurat and Picasso -- have been given by the Blocks to their city's main museum, the Art Institute of Chicago, of which he is a former president and a life trustee. James N. Wood, the museum's director, said yesterday that a portion of the auction's proceeds, in accordance with Mrs. Block's will, are to go to his museum. "We got the pick of the Block collection," he said.

This week's auctions will continue tonight, when a large collection of modern pictures that includes a Picasso self-portrait that is expected to sell for at least $2 million goes on the block at Sotheby's. Whether that auction house will prove more successful than Christie's at selling multimillion-dollar objects remains to be seen.