Joel Cash was doing his morning shoe on WINX a few days ago when his wife phoned.

"The paper boy broke the window in the screen door," she reported. "He left a note."

My wife performs a similar service for me, and her timing is uncanny. When I finally get a balky sentence rearranged in my mind and lift my fingers to keyboard it, the phone rings and the new wording for the sentence evaporates from my mind.

"The cold water faucet in the bathroom sink is beginning to drip," my joint tenant says.

"Thank you for letting me know," I say. "I'll drop everything and come home and change the washer."

"No, don't do that," she suggests. "Just fix it when you get home."

So I let these crises wait until I finish earning my day's pay, and that's what Joel did, too.

When he got home that day, he read the note and marveled that the carrier had been so honest, and had even left his telephone number.

When Joel phoned, the carrier's mother answered. "We're sorry about it, and we want to pay for the repairs," she said.

"No way," Joel said. "You raised a good kid. He's honest, and I want to compliment him and encourage him."

Later Joel wrote to tell me what a fine job David Sundell does. On rainy days, he carefully puts the paper inside the screen door. On sunny days, he just tosses it up to the door.

Joel writes: "I am sending a copy of this letter to the circulation manager and another copy to the pitching coach of the Orioles. This Sundell kid, who can throw a Post through a screen door from over 100 feet, should be scouted."

Doggone you, Joel, what you're doing is called tampering with another team's personnel. We need David's arm on our team. The Orioles can scout Baltimore Sun carriers, but don't tamper with our guys. SMALL WORLD DEPT

Hey, Joel, would you believe I was news director of WINX 25 years before you came to Washington? NO AND YES

The Iranian situation is the subject of many of your recent letters. The two categories of suggestions you make most frequently are:

1. We ought to seize all the Iranian students in this country and hold them illegally until the Iranian terrorists release the hostages they are holding illegally. In a few of these letters there is also the suggestion that we should have jailed the occupants of the Iranian embassy here instead of sending them home.

2. We ought to fine Iran a certain sum for each day the hostages are held, and we should begin paying the fines out of the Iranian assets we froze. About half these letters suggest that the fines be made retroactive to Day 1 ("the way they make their oil price increases retroactive"). The other half say President Carter should announce a deadline day on which the fines will begin. The most frequently mentioned sums are $250,000, $500,000 and $1 million per day. Some letters say "per hostage," some do not.

My reaction to these suggestions is "No" and "Yes" -- no to the first, yes to the second.

As I wrote a few days ago, American public opinion does not support illegal or brutal conduct. What good would it do to hold innocent Iranians hostage or threaten them with dire consequences? Every two-bit dictator in the world knows we would not execute innocent people -- not even in retaliation. However, the suggestions in Category 2, the ones dealing with money fines, do have merit, and I'm sure our strategists have given serious thought to them.

The ayatollah doesn't speak English but he does appear to be familiar with a couple of words -- like "million," "billion" and "dollars." TRILLION,SHMILLION

William J. Monahan of Alexandria complains that a recent Washington Post editorial said our gross national product is "$2,088.2 trillion." He doesn't say what the correct amount is, but I suspect we meant $2.0882 trillion or $2,088.2 billion.

Trillion, shmillion -- I'm not so sure a mistake of a thousandfold is really important at such a level. The human mind has difficulty understanding either quantity.

Helen Brown Strube of Hoopersville, Md., tells me that Fortune magazine once explained $1 trillion this way: "An individual spending $250,000 a day, every day of the year, would need 10,959 years to run through that much money."

Of course, the way inflation has been increasing, in a few years it might not be too difficult to spend $250,000 a day. A loaf of bread, a half-pound of hamburger, and you could blow the whole $250,000 in the express checkout line. The problem would be to figure out some way to live until December of the 10,929th year.