Way out on a limb on the money tree

The phrase ''cash flow'' has always conjured up in our private life the sound of water splashing through a bucket with holes in it. Where our cash is concerned, ''flow'' becomes a word immediately followed by ''out.''

Lately we have gotten the distressing impression that the prudent, institutional world on which we always relied for a good example has, alas, been adopting our model instead.

Is there anybody out there who can hang onto a buck for more than 10 minutes at a time?

Certainly not the banks that keep making loans on their loans to Argentina and other defaulting countries.

Certainly not the Defense Department, with its legendary squandering on nuts and bolts marked up from 99 cents to $32 - or is it $320?

One of our favorite forms of cash outflow is the telephone. But we were shocked to learn that the annual phone bill for the Pentagon is $1.3 billion, which - if we can only get a rebate on two calls to Schenectady we never made - is even worse than our own.

People and nations have always spent money energetically. History simply drips with misspent wealth. But we in the '80s are giving a new meaning to the vivid expression ''throwing money around.''

The national debt is $1.5 trillion and soaring. The Congressional Budget Office estimates it will be rising at an annual rate of around $300 billion by 1990.

To throw that kind of money around you need a world-class shot-putter, and maybe a couple of Iron Curtain weightlifters.

Then we come to the other national debt - yours and mine. The best guess is that North Americans charge $180 billion a year on just their MasterCards and Visa cards alone. This is cash flow at the torrential level of Niagara Falls, and by the end of the month many a card-carrier feels as if he is going over in a barrel.

Deficit! - the word chills the heart. Who can blame President Reagan for the single flub in his acceptance speech at Dallas - misreading ''deficit'' as ''definite''? If only the deficit were definite!

The British historian R. H. Tawney once described capitalism, at its lowest instinctual level, as ''snatching to hoard and hoarding to snatch.'' The instinct to snatch is still there: Witness all the corporate takeovers. But hoarding? What hoarding? We have all we can do to keep our hands on our credit cards and promissory notes. We certainly can't keep our hands on the cash.

Will international economy turn into one long IOU (and U and U), stored in the computers of American Express?

We trust not. But the general failure of the human race to make a dollar - or a peso or a yen - stick to its collective fingers nowadays does disturb us. It keeps economics on our mind. Even when we long to think of other subjects, we find ourself obsessed by financial questions, beginning with: ''Can you spare $ 50 till payday?'' And ending with: ''In a rich country, where the wealthiest 20 percent got 8.7 percent wealthier during the past four years, why did 6,300 people have to sleep in shelters in New York City last winter?''

Sometimes it seems as if we live in a never-never land of phantom money (more and more of it), expended on phantom goods and services (fewer and fewer of them).

If only there were some well-rounded phantom economist to explain it all - some wise and fair John Kenneth Keynes-Laffer.

But perhaps the confusion is, in fact, part of the explanation. Meaning: Economics can never explain economics because the transactions involving money - and indeed money itself - are only symbols, not realities.

In the end, the wilder the mysteries of the money game become - and they are certainly wild enough now - the more its players and spectators are driven back to John Ruskin's conclusion: ''There is no wealth but life.''