B. GERALD CANTOR, 64 who owns the largest private collection of Rodin sculpture in the world, swept into town last week to take a swing around the "Rodin Rediscovered" show at the National Gallery, which opens today. Eighty of the works in the exhibition -- including the eight-ton "Gates of Hell" -- are, or were, his.

"Stupendous! Fabulous!" he said. "What more can I say? I thought the opening at Los Angeles was something, and that the opening at Stanford was something, and the opening in New York was something. But this! I'm speechless."

Cantor is rarely speechless, but the previous openings he refered to are worth talking about. In chronological order, they are: the opening of the B.G. Cantor Sculpture Garden at the Los Angeles County Museum in 1972 ("the one with the big Balzac out front"); the B.G. Cantor Sculpture Gallery at Stanford University on April 10 ("a couple hundred works"); and, most recently, the opening of the B. G. Cantor Sculpture Center in New York on May 27. The New York event was the most unusual. It took place on the 105th floor at One World Trade Center, new home of Cantor's private skytop museum. It houses no fewer than 100 Rodin sculptures -- a fraction of the 700 Rodins he has bought and the 400 he has given away.

Open to the public by appointment, the B. Gerald Cantor Sculpture Center fills 4,000 square feet adjoining the offices of Cantor, Fitzgerald Group Ltd., the financial holding company that made Cantor rich enough to support his 35-year passion for Rodin. "We're in the next Guinness Book of World Records," revealed Cantor proudly: "the highest museum in the world. In fact, we're the highest floor for anything except restaurants. The National Gallery is greater, but we're higher.

"But it hasn't been easy." he added. "Before we opened I had a terrible dream that "The Thinker" fell down 105 floors to the ground. What a nightmare!"

The "B" in B. Gerald Cantor stands for Bernard. "Everybody who knows me calls me Bernie," he explains. A hometown boy from NYU, Bernie began his love affair with Rodin in 1945, just after he got out of the army. "I walked into the Metropolitan Museum one day, saw Rodin's 'Hand of God,' and my head turned on." Cantor was not born rich, "no, ma'am," he says. "But I learned that to be a collector you need two things: first you need money, then you need taste."

Cantor credits Cecile Goldscheider, former curator of the Musee Rodin in Paris, with developing his taste and helping him to fully understand Rodin. "We had a great love affair, she and I and Rodin," jokes Cantor. It was the Musee Rodin that gave Cantor the original Rodin plaster of "Hand of God" (on view in the National Gallery show) to thank him for perpetuating the memory of Rodin through gifts of sculpture to museums all over the world, and through grants to Rodin scholars through the Cantor, Fitzgerald Rodin Research Fund. Many of the newest Cantor-funded findings have been published in the Rodin catalogue that accompanies "Rodin Rediscovered."

"Collecting became an obsession, a sickness," admits Cantor. But his wife -- unlike most wives of men obsessed -- does not resent the time and money he lavishes upon Rodin. In fact, Iris Cantor -- with Bruce Bassett -- has just finished producing a Cantor-funded, feature-length movie on the "Gates of Hell," the fifth, most recent and best bronze casting of Rodin's most ambitious project. Cantor also commissioned the casting of those "Gates" now in the National Gallery show (insured value: $5 million), and they will ultimately join his other Rodin gifts to Stanford. Why Stanford?

"Two reasons," says Cantor. "The first is Prof. Albert Elsen, the world's leading scholar on Rodin; and my friend for many years, Peter S. Bing, president of the Stanford trustees." Cantor has also made substantial gifts to 17 colleges and universities; 27 American museums, including the Museum of Modern Art in New York, the Norton Simon Museum, Pasadena, Calif., and the Museum of Fine Arts, Houston; and six foreign museums, including the Israel Museum, Jerusalem and the Vatican Museum, Rome.

Cantor was eager to discuss the issue of "originality" in Rodin's bronze sculpture, no suprise considering the fact that many of his own bronzes were cast by the Musee Rodin after the artist's death. Some purists have suggested that such posthumous casts -- even if taken from Rodin's own plasters -- are not "originals." "When you get right down to it," says Cantor, "almost nothing we have -- except the terra cottas and the drawings -- are originals by that definition."

"I insisted upon this discussion, and said, 'Let's finally get it out in the open,'" says Cantor. As a result, the "Rodin Rediscovered" catalogue carries a full discussion of Rodin and his army of collaborators -- at one point he employed 50 helpers -- including reductioneurs who made the plasters smaller and larger (after Rodin had sculpted them in clay); founders who cast them, and carvers who actually executed the marble sculptures from clay or plaster models. The further question of counterfiets, or "surmoulages" -- unauthorized bronze castings made from existing bronze castings, rather from Rodin's original plasters -- has done much to muddy the Rodin market since the artist's death.

Cantor still remembers the shock of his first encounter with multiple copies of the same work -- a shock that many have experienced with Rodin. "Can you imagine how I felt after seeing the marble 'Hand of God' at the Met in 1945, and then -- two years later -- seeing a 5 1/2-inch-tall bronze 'Hand of God' in a gallery on Madison Avenue? I couldn't believe my eyes, and went to the library to check it out. There I learned that there had been reductions and enlargements of sculpture since ancient times, and that being and enlarger or reductioneur of sculpture was a highly skilled profession in France. I realized that this little bronze was an original work, and went back and bought it for $70. I later found I'd overpaid."

"But let's take 'The Thinker,'" says Cantor. "'The Gates of Hell' were never cast in Rodin's lifetime, and 'The Thinker' -- originally conceived to go on the lintel over the 'Gates' -- was first made in a plaster 28 inches high. Subsequently, when people came to see Rodin, they saw the plaster and wanted a bigger version, so he had it enlarged by M. Labosse, his enlarger and reductioneur, and then cast. There are now roughly 25 to 30 bronze enlargements of 'The Thinker','" says Cantor, "and also smaller 'Thinkers' -- I don't know how many -- all about 15 inches high. I have one. They come up for sale from time to time."

"When Rodin died," explains Cantor, "he left everything to the Rodin Museum in Paris, including all rights to his work. As a result, they -- and they alone -- have the right to make castings, so long as no more than 12 exist. In other words, if the records indicate that there are eight extant bronzes of a particular work, they will cast four more. If a work has never been cast, the Rodin Museum can -- if they wish -- cast an edition of 12. Of course they would never make a reduction or enlargement of an existing work, or make a new cast from an existing work. No way. Those would be rip-offs."

Which brought Cantor angrily to the subject of the late Nelson Rockefeller's venture into the manufacturing of art reproductions.

"Nelson Rockefeller made reproductions of innumerable art objects, and obtained rights from some artists to do it. But he also made copies of three Rodin casts he owned -- "The Thinker," "Age of Bronze" and "Torso of Adele." His craftsmen put plastor on the bronze, made a new mold, cast a few hundred new bronzes and got away with it. The reproduction was so good that I'm telling you, I couldn't tell the difference." Asked whether permission had been obtained from the Musee Rodin to make these reproductions, Jean Chatelaine, former director of the Museums of France, and Monique Laurent, conservator of the Musee Rodin, both answered emphatically: "Absolutely not."

A call to the Rockefeller Collection, a shop that still holds out bravely on East 57th Street in Manhattan, confirmed that they do, indeed, have three Rodin reproductions for sale, as reported by Cantor, all made from bronzes owned by Rockefeller. They confirmed that a mold was taken from each of these works and cast by the lost-wax method. They also said that each object is marked clearly on the bottom with an "NCR."

"Except for our markings and our logo, they are almost undistinguishable from the originals," said the store representative. Cast in so-called "limited editions" of between 150 and 250 each, these reproductions cost $1,950 for the "Torso of Adele," and $7,500 each for "Age of Bronze" and "The Thinker."

Cantor and Prof. Elsen of Stanford were at the forefront of a battle to stop the making of such surmoulages -- bronze castings made from bronze castings -- a practice which the College Art Association condemned as unethical in its 1974 "Statement on Standards for Sculptural Reproduction and Preventive Measures to Combat Unethical Casting in Bronze."

"It's the national standard," said Elsen of the document he helped to write. "In Rockefeller's case, the faults were inadequate labeling and not making changes in either the size, material or surface finish that would have made perfectly clear that these wee reproductions. These copies have already been a boon to unscrupulous people," said Elsen, recounting the day that Cantor picked up a cast of "Adele" in a shop in Paris not long ago, and black shoe polish -- obviously meant to cover the "NCR" -- came off on his hands. "I said these things would create mischief, and they have."

Exactly how much Cantor has spent on Rodin, his life and art, even Cantor isn't sure, but he has no doubts about why he's doing it, apart from his own pleasure. "I think Rodin is misunderstood -- lost in the mire," says the man who has been called, he says proudly, "Rodin apostle." "They remembered Michalangelo, but they forgot Rodin. It's high time he was rediscovered."

But does Cantor think Rodin is as good as Michelangelo?

He thinks hard for a minute. "He's second best," says Cantor finally, "and that's for sure."