Nelson A. Rockefeller has a lot of money - he is, as the song says, as "rich as Rockefeller" - but he returned to town yesterday in order to make more.

Once he was vice president of the United States. Today he is a salesman. Rockefeller, 70, is good at his new trade.

Like most successful salesmen, he admires his own wares. "Isn't that just beautiful?" he asks, beaming with delight at a photo he is peddling. "The lighting is the best that I have ever seen!" The photo, a Cibachrome he calls it, shows a 1910 canvas by Picasso. You can buy it, framed - the photo, not the painting - for $850.

It is on sale at Neiman-Marcus, upstairs in the gift shop. So, too, are the plates, the andirons and status and candlesticks he's selling. Rockefeller calls them "beautiful reproductions of great art."

He began collecting half a century ago, and he calculates he now owns some 16,000 pieces - European porcelains, American weathervanes, Chinese porcelains, pictures by Cezanne, Degas, Bonnard and many other masters, and tables, earrings and toys. His new catalogue - his first, he says there will be more - offers reproductions of 124 and includes a little of everything. Most works are being made in unlimited editions.

How should one address him? Should you call him Governor? Or Mr. Vice President? "Hey, just call me Nelson, he says, sticking out his hand.

Several of his old friends here believe they can explain his going into business. "He's competing with his brothers," said one of them. "All those years while they were out there earning money, he was busy spending it on political campaigns. He is trying to replenish the Rockefeller coffers. He's selling his houses and his reproductions. He is trying to catch up."

"That may be an underlying motive," Rockefeller says. "But I happen to feel art is a major force in people's lives. You need to lose yourself, to find tranquility in beauty. Art is a major joy in my life. It's a joy I want to share."

He has begun to share it by entering what he calls "big business." Already he has hired 13 people, and he has mailed out 470,000 copies of a gold-and-purple mail order catalogue. "Truly great works of art have withstood the test of time and steadily gained in appreciation . . . Indeed, art is even being purchased as a hedge against inflation," his "Dear Friend" note explains.

Rockefeller knows that many in the art world sneer at the idea of prestige reproductions. "I expected a lot more criticism," he said.

"His pieces cost as much as many respectable originals," observed Joshua C. Taylor, director of the National Collection of Fine Arts. "I don't object to simple reproductions, but his pretend to be surrogates for the actual objects. Why don't people go out, use their eyes, and buy works of art on their own?"

Rockefeller's bronzes, copies cast from Rodins and Nadelmans and African originals, seem to be good copies (some cost $7,500), but the "paintings" he is selling announce themselves as phonies even at first glance. The shadow-casting brushstrokes and the threads of woven canvas are seen in three dimensions when one looks at an original. In Rockefeller's photos they've been flattened into two.

"I happen to have a Cibachrome in my home right now. Nobody who comes in can tell the difference," Rockefeller says.

"The difference between an original and a copy might appear quite narrow - if you look at art as decoration," said J. Carter Brown, the National Gallery's director. "But scholars and museums see that gap as a chasm. Museums have an obligation to authenticity and history. Nelson Rockefeller is a private individual, not an art museum. This is a free society. He can do anything he wants."

"The art of reproduction has a very long history," Rockefeller writes in his catalogue. "The ancient Romans had their best sculptors create copies of outstanding pieces of Greek sculpture . . . The same was true in China." But their pieces were created by hand, not by mass-production methods.

During his tenure as vice president, when Rockefeller lived there, he was very rarely seen in galleries or museums, but he did keep up with art through photographic reproductions. "I read catalogues every night," he said. At home he eats off Meissen plates that are copies of antiques. At his office he hangs Cibachromes. "I have increasingly, myself, shifted over to reproductions," Rockefeller says.

"Sales," he continues, "are going very well. My 11-year-old son said the other day, 'Dad, everybody in school is talking about what you're doing.' The response has been terrific. I have already been to Dallas. This is my second store appearance. It also is the first time in 40 years I've been in Washington on anything but public service."

"Some people," Rockefeller said, "say that selling reproductions violates the dollar value of the original work of art. I don't think so. My feeling is that it will enhance the value. If the public gets to know, say, Chinese export porcelain, the demand for the originals is liable to increase.

Rockefeller paused before a glass case of Boehm birds. "That's natural history, not art," he says. "Hey, thanks for coming by," he adds. Returning to the gift shop, he makes eye contact with the shoppers and waves at the crowds.