A. Alfred Taubman, who already has spent a considerable amount of money buying paintings at Sotheby Parke Bernet, apparently has decided he might as well buy the whole company.

Taubman, a customer of Sotheby's for some years, said "mutual friends" of his and Sotheby's had suggested he buy the company. "It came about partly because of my relationship as a customer. It's a unique opportunity for someone like myself. I wouldn't have a chance if the company were not in the need of a friend."

Taubman, reached by telephone in London late last night, seemed as excited about owning the 239-year-old-company as if someone had given him a major Picasso painting.

"I feel humble about the opportunity to acquire this company, whose name has become generic, a synonyn, for auction," said Taubman, who said he had spent the evening at a castle outside London. "It's a major business opportunity. And I think I could be helpful in holding on to its financial strength, though it's doing fine without me."

Taubman, often described as the wealthiest man in Michigan, is an art collector, philanthropist, real estate developer and owner of the Michigan Panthers, a team in the new U.S. Football League. An architect by training, he is known here as the developer of the Lakeforest shopping mall in Gaithersburg and Fair Oaks in Fairfax County as well as president and trustee of the Smithsonian's Archives of American Art.

The purchase, which would include Sotheby's International Realty Corp., could cost more than $100 million. Under British stock regulations, the earliest Taubman could take control would be in October.

Sotheby's management in London has welcomed Taubman, whose takeover plans were announced by Sotheby's Thursday, as a "white knight," and has promised to recommend that he be allowed to purchase stock for a takeover. Because of the cyclic nature of the art business, Taubman said he thought Sotheby's should be privately rather than publicly held.

Taubman said he had been talking with Sotheby directors for the past month but had come to London only a week ago.

Despite earlier reports, he said Sotheby's hadn't been snobbish about the possibility of being American-owned. "For all practical purposes, the majority of shares are already held by Americans. Though the company is London-based, 50 percent of its world business is in the United States. I don't have any intention of moving it. It would be rather ridiculous to change its seat of management."

Earlier, Sotheby's had hotly protested a takeover bid from two other Americans, Marshall Cogan and Stephen Swid, who head New Jersey-based Knoll International, manufacturer of a prestigious modern furniture line. Cogan serves as chairman of the American Council for the Arts.

Cogan and Swid had bought 29 percent of the Sotheby's stock before the prospective purchase was referred to the British Monopolies and Mergers Commission. On May 5, the commission stopped the takeover for six months to consider the matter.

A Knoll spokesman yesterday reaffirmed the corporation's intentions to "make a further offer."

In contrast to the curled lip that Sotheby's staff and directors had offered Cogan and Swid, they have burst out with welcoming smiles for their old customer.

Taubman said if he's allowed to buy the company he'll be a director but "I don't expect to run Sotheby's."

He said of the staff: "I'm hoping they'll assure me they want to stay on."

He said he could afford to pay cash for the company, but didn't rule out some help from other investors. In the past, Taubman has made financial investments with industrialist Max Fisher and auto manufacturer Henry Ford II. He said last night for "now I'm acting on my own."

Julian Thompson, chairman of Sotheby's United Kingdom and European companies, said in a telephone interview from London that "Mr. Taubman has met our senior experts and board. His approach and the chemistry is excellent. Everyone he's met feel they can work with him very well. It is important that we like him. But the way he has gone about the purchase has been extremely important. The other bidders' approach was very insensitive."

Taubman said he thought the problem with Knoll's approach was "they took on the form of a raider rather than someone attempting to work with the company."

Taubman, 58, is counted as a man of well-rounded interests. The Taubman Co. Inc., in Troy, Mich., is the largest shopping center developer in the country. He also heads A&W Restaurants, which owns more than 800 restaurants throughout the United States.

Part of his credentials as Sotheby's white knight are the many offices he holds in the art world, including trustee of the Whitney Museum in New York, a member of the Arts Commission (the Detroit Institute of Arts), trustee of the Michigan Foundation for the Arts and director of the Detroit Symphony Orchestra.

Sotheby's, which had a bad year in 1982, expects to be in the black by October, according to Liz Robbins, a New York spokeswoman for the company.

In London, Thompson said, "The recession is over in the art market."