WARREN AVIS has sold his car rental business, in case you missed that news item of 1954, for a few million and is now into real estate, behavior and flowers.

He was in town this week looking at his investment in the town-house condominiums at the old paper mill on Grace Street in Georgetown.

Settled steady persons in the neighborhood sometimes come unhinged at the thought of it - all those houses where the nice ghastly ruin of the mill used to be (with water and rotting wood in the old power house: a real landmark for squalor that was, of course, admired by many Georgetowners).

"Sailed through the Fine Arts Commision without any trouble at all," said Avis, who observed later on the Business should get along with government, because if government becomes an enemy, government always wins.

"Look who won in the fight of church and state," he observed. Indeed, the lessons of King Henry II and his courts are utterly relevant.

Avis has invested about $800,000 so far in Avis Flowers Worldwide, he was saying.

You call information and get the number (until the phone company gets it in a new directory) and order some specific item to be sent to Detroit, say.

Of course you can do without Avis already, but he thinks the sophisticated management (he was, he does not mind saying, the first guy to see the need for cars that could be rented at airport) will make his service better than another. He will, you are sure while listening to him, try harder,

He sat in the old power house of the old mill. The power house renovation (getting the water out, etc.) cost $350,000, he said, and is now an office which must have a horrendous heating bill, since it is a great room like a train station. It will become a restaurant, Avis said, and who will be able to resist the view of the Potomac and the general air? He is right. Some people dearly love to eat in barns, warehouse, horse stalls, windmills, bank vaults or any place that didn't used to be foody.

He wears neat tailor-made shirts and dark suits cut a bit on the youthful side, with almost white Pinstripes. Somewhat like France or California, I thought, where you never grow old but retain to the last a certain dash.

His mother is 98, lives n Michigan (where Avis has several hundred acres out from Ann Arbor and a behavior research project of some kind going on there) and when she sees her son she thinks it's great that he's slender, but is his skin color right?

"She thinks you should drink more milk? A lot of mothers swear by milk and are forever saying you should drink more," it was suggested.

"I got my cholesterol down to 100 in no time," said Avis, "by cutting out a lot of meat. Eat a lot of chicken and fish. I tried cutting out the eggs and cheese, but it was the meat that did it. Cut down the meat and you cut down cholesterol."

Everybody knows about Avis' house in Acapulco. I was afraid, therefore, to ask about it. He also has an apartment on Fifth Avenue, the bedroom of which is deep blue. (Blue is a favorite color of fat people because it is heavy, not to appressive, and makes them fell buoyant, but that cannot be the reason for Avis who perhaps simply likes deep blue.)

Avis is a great believer in courtesy. Why else do you think he got into the flower business? Certainly not money.

"I could retire and live all over the place. But what would I do in the morning?" he said.

Good question. One often wonders the same thing.

It is a courteous thing to send flowers to friends out of town, and Avis hopes to double the courtesy now current. This has meant getting onto fields of guaranteed rose production in California, guaranteed florist shop credit, and other complexities, none of which worries Avis in the least.

As he says he "conceptual" and loves to cut through things with manageable abstraction instead of a vast clutter of details.

"How many problems could you identify at The Washington Post?" he said suddenly. "Not to keep you waiting, let's say maybe 20."

"Wrong," he said. "No more than five. There are never more than five."

All this time he doodled and made assertive marns on some paper, as they do in the better sort of board meetings, and gave example of how to organize problems:

"Take transportation in Washington," he said, leaving the poor Post alone, "you might say you have an automobile or highway problem, a Metro bus problem, a subway problem. But no. You have one problem, transportation."

Still and all, I muttered in my head, sooner or later somebody is going to have to fiddle around with water in the subways, and bus drivers who don't show up and buses that don't, therefore, run.

It is better, surely, to be the guy who solves Transportation than to be the guy who solves the bus drivers and the subway leaks.

I think tycoons are tycoons not because they conceptualize better, but for some less grand reason, such as the ability to get along with everybody and not make wisecracks.

Never met a more affable man or one who sees things more clearly, and I liked seeing how the other half lives.

Meanwhile, to end on a cosmic note, my poor luna moth died while emerging from his cocoon. The pupa gots its antennae through about 5 p.m., then rested until 10. From 10 till midnight he chewed steadily - I had him in a mixing bowl under a lamp - then I turned off the light and went to bed. Yesterday morning he was weak, and I turned on the light and gave him daffodil stems for his legs to grab and pull. He didn't make it.

Why is such a thing so depressing? Not because it reminds us of death, I suspect, but because he died and the major joys of mothdom he never tasted. Other moths, from similar cocoons, hatched all right. But it's like the lost sheep. You take it harder.

Grief fortunately does not last in its sharp forms and tomorrow to fresh woods and pastures new.