ONCE, AT THE SORT of Washington dinner party Spiro Agnew warned you about, a group of us planned a question to be asked the next day at press conference given by President Carter. It was the question that produced his "life is not fair" remark on abortion which in turn produced a running news story for something like three days. Not bad for a dinner party.

With that success in mind, I have been framing a question to be put to the president at the Iowa debates with Jerry Brown and Edward M. Kennedy which now, unfortunately, have been scuttled by none other than the president himself. I was not sure, really, if I would have preferred Kennedy or Brown to ask the question, but there is something about it -- its bluntness, maybe -- that makes me feel that Brown could have been perfect. Imagine him sneering and then snarling and then asking the following question: i

"With all due respect, sir, we still have 13 percent inflation and still have 5.8 percent unemployment and we still don't have a viable energy policy and Russian troops are still in Cuba and the dollar is still falling and gold is going up and the hostages, sir, are still in Tehran. Just what have you done?"

Now I, for one, would not have the nerve to ask such a question. It is intemperate and uncivil, but it needs to be asked and it is one of the reasons why cancellation of the debate is such a shame. The one thing about a presidential comapaign, even one that starts prematurely and goes almost nowhere, is that it is supposed to hold incumbents responsible for their actions.

But we still have no debate. The president has decide this, and his reasons, to be fair, are good ones. The situation in Iran is critical and the situation in Afghanistan may, in the long run, turn out to be even more critical. It is disingenuous to point out, as some have done, that on the very same day President Carter pulled out of the Iowa debate he was on the phone, calling prospective voters in that very same state, asking them for their support in the caucus.

That is not the same as going to Iowa for a debate. At the very least, it is a difference the Iranians understand and it does eliminate the chances that Carter would say something that would only worsen matters for the hostages.

So there is reason to be cautious. Iowa, after all, is only Iowa and a caucus state at that. It is not a primary state and it is not, for the sake of argument, a biggie like New York or California. Still, you have to wonder if the president would have made the same decision had be been behind Senator Kennedy in the polls, instead of enjoying an approximate 32-point bulge at the end of December, and if it wasn't evident that he could not do the sort of damage to Kennedy that Kennedy has already done to himself. In fact, the Kennedy slide has gone so far, he could probably only help himself in a debate, providing at the very least that he is not the oral bungler that he has lately been made out to be.

Anyway, back to my question. It is a fair one, a blunt one, for sure, but one that needs to be answered. The president has been given a grace period by the events in Iran, but he cannot spend the rest of the campaign in the White House. He has to come out sometime and account for what he has done during his term of office. He has, I know, some pretty good answers to those questions. It would be wonderful to hear them.

But at the moment, he's not talking. He is controlling the political process, setting the agenda, deciding what is political and what is not, and the media, by and large, have gone along. They have decided, for instance that a day when the White House appears to do nothing is bigger news than whatever is said by Kennedy or Brown or, for instance, John Anderson, the Illinois Republican with something fresh to say. It is the lazy way for us news guys and it is also a signal lesson in why the incumbency is so important.

So kiss the Iowa debates goodby. It's not that big a loss anyway. There are plenty of primaries down the road -- plenty of chances for debate. Iran is important and so is Afghanistan but so, for that matter, is the American political process -- more important, really, than all the rest. It can't be put on a shelf, suspended at the determination of the president when some crisis keeps him glued to the White House.

The campaign clock ticks on and soon the time will come to answer questions. Come on out, Mister President. We have some questions for you.