Dr. Armand Hammer, the 80-year-old multimillionaire (oil, whiskey, cattle, pencils, medical supplies) strides out of his Blue Room reception at the White House, and into the Green Room. He reaches out to shake hands. He does not let go.

"We'll find a place to talk," he says.

He does not let go, even to pull a straight-back chair away from the wall. This must be the determination that makes fortunes.

"Yes," he says, relenting at last. "I'm feeling fine. Friends tell me I look younger than I did several years ago. I swim half an hour every morning - have a swimming pool at home, but then I'm not home much.

"I just flew in from Bolivia where I met the new president, who was very different than I expected - I'd expected to see a typical South American dictator, and he was very modest. Says he's going to hold elections. There's oil down there, lots of it . . ."

And so on, a tap-dance of names and places: just back from Poland, spent the weekend with party chief Edward Gierek, and he's on his way to New York to collect an honorary degree from Columbia: "Igave them $5 million, you see."

Hammer, who is chairman of Occidental Petroleum, and donator of millions of dollars in art to both the United States and Russia, has flown here in his Gulfstream II private jet to be thanked for donating a painting - "Cincinnati Enquirer, 1888," by 19th-century trompe-l' oeil master William Harnett - to the White House.

The mighty of the arts and museums are here in force: S. Dillon Ripley from the Smithsonian, Carter Brown from the National Gallery, Livingston Biddle from the National Endowment for the Arts. After Mrs. Carter's speech of thanks, all retire to the Blue Room.

Despite the intoxications of iced tea and watercress sandwiches, however, Hammer finds a deserted corner of the neighboring Green Room, and sails into conversation.

"I bought the painting from Bill Middendorf in February," he says, referring to his business cohort, the former secretary of the Navy. "He wanted $500,000 for it, but I got it for four. You know a Bingham went for over a million, and I think this is as good as that."

Actually, the painting has been hanging snugly in the White House for five years, most recently in the West Sitting Hall, so the ceremony was largely an exercise in accounting and symbolism. But then, symbolism is what Dr. Hammer is so good at.

Take, for instance, the recent Francis Crawford affair. We arrest a Russian for spying; the Soviets signal their protest by arresting an American businessman for currency violations. Hammer, having organized Soviet-American swap meets for everything from fertilizer to Old Masters, knows the drill.

"I was asked to write to Mr. Brezhnev," says Hammer, who has befriended every Russian leader since Lenin. "When I ran into him in Yalta, recently, he told me that it looked like the evidence was against Crawford. I said that American businessmen were very disturbed, and he assured me Crawford would be allowed to leave the country."

Hammer, looking natty in the new shorter-point collar, keeps his eyes moving like those of a delighted chess player who can't wait for you to stop struggling so he can put you in check, again. Everything, it seems, is wonderfully clear.

With the good news relayed from Russia and Bolivia, he moves on to Mexico, where he's afraid "we've irritated them by quibbling over the price of gas. You see, Mexican oil could solve half of our energy needs.

"I was down there talking to the president, and when I came out of the office, what did I see sitting in his waiting room? Nothing but Japanese! They want it too, of course."

Hammer can't understand why, if we can put a man on the moon, we can't get the oil out of oil shale, economically; and he worries that we don't take enough chances: "If Roosevelt hadn't taken a chance on the Manhattan Project, the Germans would have gotten the atom bomb and we'd all be slaves of Hitler now. Same thing with synthetic rubber. I was in the alcohol business then, you see . . ."

Larger number of pin-striped men seem to be checking gold watches and grumbling about appointments on "the Hill," but Hammer is glad to explain how he relaxes.

"This is how I relax," he says, sweeping a hand across the panorama of Washingtonians flexing terminal grins around the Blue and Green rooms as they broke power over the watercress.

"This is what keeps my glands flowing. Of course, I have a way of taking naps for 10 minutes, anywhere at all. Napoleon could do it too. I just shut my eyes and think I'm lying in a forest listening to a babbling brook. I could do it right here!" he says, and actually tilts his head over his shoulder to demonstrate.

Then the men with the watches prevail and Dr. Hammer is off to say his goodbyes in the Blue Room, giving the impression, even as he strolls, of a man running - or, just possibly, even as he runs, of a man strolling.