Here is a tale of two countries set at the Corcoran Gallery of Art last night:

The American businessman approaches the Nigerian businessman and begins chatting. "I'm in petro-chemicals," says the American. "It's great for killing mosquitoes around crops. Let's have lunch. We can talk about it."

"Oh?" the Nigerian asks. "Tell me how that works."

The American explains enthusiastically. The Nigerian listens. "Great at killing mosquitoes," the American concludes.

"But how does it work on flies?" the Nigerian asks.

"Flies?" says the American. "It doesn't kill flies."

"Well, we don't have mosquitoes -- just flies," says the Nigerian. "But we can still have lunch."

And so the conversations sprang up between tables of steak tartare and clams on the half shell at the reception hosted by Mobil Oil, the Corcoran Gallery and the Museum of African Art for the much-heralded "Treasures of Ancient Nigeria." The exhibit, jointly sponsored by the Museum of African Art and the Corcoran, opens at the Corcoran tomorrow.

Downstairs, smack in the middle of the gallery, was a hugh Christmas tree. Upstairs, through rooms painted mustard and deep orange, were the African works, "majestic" -- as one guest put it -- in glass cubicles. Wandering through both floors were Corcoran trustees and Mobil officials, local community leaders and Nigerians -- from the embassy as well as just in from the country.

Downstairs at the entrance was Alex Massad, executive vice president of Mobil Oil. His mind, he admitted, was wandering away from art. He was thinking about Canada. Specifically, he was thinking about the Canadian government's decision to take over 25 percent of foreign oil operations. Mobil is the fourth-largest oil producer in Canada. Still he was gamely shaking hands. He spotted a man with an infant.

"Oh, I'm delighted you brought our youngest visitor," Massad said.

"He wants to learn about Nigerian art," the father explained.

"I'm Alex Massad."

"Mayor Barry."

Upstairs in the exhibit, Ekpo Eyo, Nigeria's director of museums, in bright white agbada, looked up at the ceiling. "Oh," he shrugged calmly, "it looks all right. Yes, it's pretty well done. I wasn't sure how it would look at night." He nodded approvingly. Of course, he'd been here several months ago to make sure the Corcoran was more than all right. He had chosen the Corcoran over the Museum of African Art. "Security, that's all," he had said, smiling.

"Well, you know what they say about Africa," he said, his words clipped, rather British. "A country without history, without culture, without art. You'll notice there are no wood carvings here -- because people think of African art as all wood carvings. I think people will be startled when they see this. We have shown them history. They must make their own conclusions."

Lee Kimche, head of the Institute for Museum Services, came over, beaming. "Remember me from the Soviet Union?"

"Oh!" Eyo exclaimed softly. "Good to see you."

Downstairs and upstairs, Corcoran director Peter Marzio hopped briskly around, introducing Mobil officials, showing guests through the gallery.

Upstairs, Warren Robbins, director of the Museum of African Art on Capitol Hill, pondered soapstones and bronzes.

"They're like old friends," he said, smiling. "Sure, we would love to have had it at our museum. But we're not unhappy it's here. We felt we didn't have enough space, so we cooperated with the Corcoran. It's a beautiful installation. And it may attract large enough crowds that would have shaken our small foundations." He laughed. "But what a way to go."

Former mayor Walter Washington and his wife, Bennetta, were attracting old friends downstairs -- someone from the Department of Labor, someone else from the City Council. There was some talk of Sterling Tucker's starting up his campaign for mayor. After he saw the exhibit, Washington was overheard remarking, "It shows we were here even before the Lord was here."

Mayor Marion Barry was showing off 6-month-old Marion Christopher, who observed the politics of it all silently, wide-eyed. Effi Barry looked on. As they walked up the marble stairs, the Howard Devron Shoreham Strings Ensemble broke into "Rock a Bye Baby." The two mayor, past and present, met on the stairs. More oohing over baby. By the time the Barrys reached the fabled Benin bronzes in the exhibit, Marion Christopher was fast asleep. t