"Georgia O'Keeffe painted pineapples for Dole Pineapple in the early part of her career," said Henry Robert, director of the Montgomery Museum of Fine Arts in Montgomery, Ala. "Not many people know that."

The advertising angle was one explanation offered last night of why American corporations have chosen to become art patrons and why 90 of their artworks have been collected into the "Art, Inc." exhibit, at the Corcoran Gallery. Of the 30 corporations whose paintings are included, only a handful sent representatives to last night's opening.

But they were enough for Winton "Red" Blount, postmaster general during Richard Nixon's first term and president of Blount, Inc., who helped develop the idea of the show.

'This show might even go to Leningrad!" proclaimed Blount, who was clearly enjoying the night, as he talked to Russia's cultural attache here, Anatoliy Dyuzhev.

About 100 people, including corporate executives, a few congresspeople (including presidential hopeful Sen. Bob Dole of Kansas) and Secretary of Commerce Juanita Kreps, were guests at a candlelight dinner that lingered so long in a skylighted gallery that they could hardly see their plates.

But they raised the lights long enough for numerous champagne toasts to Blount and then to Kreps, who has hosted a small party before the dinner in her private office.

"The earliest art museums, the earliest art schools, were funded not by the federal government but at least in part by American businessmen," said Corcoran Gallery Director Peter Marzio during his toast.

Only one political jab found its way into the toasts, when one guest said of Blount, "He's a very successful businessman and he's a supporter of John Connally. For those of us in the administration, we hope to see his increased interest in the arts and decreased interest in politics."

The roomful of people guffawed, including Carter media adviser Gerald Rafshoon, sitting not far from Blount.

Most executives shied away from saying they collected the art for investment. In fact, one executive whose company's artwork has increased in value four- and five-fold said the increase dismays him: "Then I can't enjoy it."

"We hang our art all over the building," said American Republic Insurance Company's chairman of the board, Watson Powell Jr. "In every office, every work area, even powder rooms. "We're very fussy about that."

Powell, who personally collected the art that hangs in his building, went to Mexico and Europe for the 500 pieces. "When we first started, the architects who did our building were really afraid of what we were going to buy."

Powell's company's collection includes Andy Warhol's portrait of Watson Powell (the current chairman's father), done in 1964, which is in the Corcoran exhibit.

"My father hated it," said Powell of the typical Warhol multiple picture silkscreen.

"He just wasn't ready for it," explained Powell Jr.'s wife Louise.

There were some problems, in putting the exhibit together, said Walter Hopps, former curator of the Corcoran.

"We couldn't get clearnance to get into some of the companies where the art was hanging. They were mainly southern California companies in the nuclear whatever business. The companies had to figure out when they weren't having high security meetings in the rooms where the paintings were. That was pretty bicarre."

And then John Deere, which did lend some paintings, has a classic Grant Wood painting of a field scene that people were always begging to borrow.

"Everyone wants that Grant Wood for exhibit," said Hopps. "The chairman of the board finally threw up his hands and said he wanted it for one week while he was still chairman of the board." CAPTION: Picture 1, Winton Blount and Juanita Kreps at last night's pre-dinner party; by Harry Naltchayan; Picture 2, "The Kansas City Spirit" by Norman Rockwell, from the Corcoran's "Art, Inc." show