If there is some question in your mind about the impact of messages broadcast by radio stations, consider the sudden explosion of interest in sending holiday cards to the American hostages being held in Tehran.

It is not at all certain where the idea originated, although some evidence points to WGN in Chicago. We do know that an announcer there suggested to his listeners that they send holiday cards to the hostages to show them that we haven't forgotten them and are still working for their release.

The stuggestion generated instant and massive reaction. Thousands of people began phoning thousands of other people to help spread the word. The wire services carried news reports about the idea. When announcers in cities all over America saw the news items, they said to themselves, "A great idea! I'm going to give it a boost, too.

Les Carpenter of WJMD, Bethesda, tells me that when the idea was mentioned on that station, "Every one of our telephone lines lit up at once and remained busy for two hours as people called in to say 'Thanks' for the suggestion or to ask us to repeat the address." Other local broadcasters got similar reactions from their listeners.

In less than a week, hundreds of thousands of greeting cards had entered the mail pipeline. Some bore correct addresses, some didn't. Some carried 15-cent stamps, some carried more postage, a few were unstamped.

United States Postal Service executives had to make some quick decisions on how to handle this flood of mail. They did just what you and I would have done. They passed the word that an attempt should be made to deliver everything addressed to the hostages, whether or not each letter bore enough postage.

Meanwhile, hasty meetings were also convened at the Department of State. What emerged was handsoff policy: "We neither encourage nor discourage the sending of cards."

Privately, one old hand at State said to me, "We don't have the foggiest idea of whether the cards will be delivered or thrown into the trash. We have absolutely no way to know what will happen to mail addressed to the hostages. The Iranians have permitted us no contact with the hostages. We're not even sure they're still at the embassy, and my own personal guess is that people who are capable of such an outrageous breach of conduct are also capable of refusing to let the hostages know that a million cards have arrived addressed to them."

I had a gut feeling that he was right, and that it would do about as much good to send a card to the hostages as it would do to wish Ayatollah Khomeini a merry Christmas. My mental image of the Ayatollah in a merry mood was a little out of focus.

"The American people have responded positively to the holiday card idea because they feel a tremendous urge to do something," I said. "Do you have any suggestions?"

"Yes," was the reply. "A few days ago, the families of the hostages unanimously endorsed the idea of sending letters, postcards and petitions to the Iranian Embassy in Washington to demand that the hostages be freed immediately. If the American people were to flood the Iranian embassy here with such cards and letters, I'm sure the message would get back to Tehran in a hurry. The Iranian leaders would be made aware of the intensity of American public opinion."

The address is: Embassy of Iran, 3005 Massachusetts Ave. Nw, Washington, D.C. 20008.

I don't know how much good our letters and petitions will do, but at least we do know that the Swift Couriers of the postal service will deliver mail addressed to the Ayatollah's embassy here, and we do know that the proper amount of postage for a domestic letter is 15 cents.

Let's drown the ayatollah in a blizzard of protest. You don't have to buy a card in a store. Your own words set down on a single sheet of paper will be even more effective.

If some of those 34-year-old students learned to read before they dropped out of class to major in terrorism, perhaps they'll get the message that the patience of the American people is running thin. COMPULSORY EDUCATION

W. M. O'C. writes: "Everybody wants to 'get even' with the Iranians after we get the hostages out. Even President Carter, a patient and charitable man, has indicated that just releasing the hostages won't be enough.

"I can't think of any act of revenge that would please me more than insisting that those bogus students really attend a good school, and remain there until they understand why the world condemns them for their reprehensible actions."

The suggestion has merit, yet may do no good. You can lead a student to the fountain of knowledge, but you can't make him drink. Or think.