Big issue deflated

There was really only one issue, largely unspoken, that could have turned the election around: The President's age. He buried that problem once and for all with a quip. He even got a big laugh from his toughest audience - Walter Mondale.

Ronald Reagan once again showed that he is the master of the ''masterstroke'' in TV debate. In the 1980s primary race, he destroyed George Bush by declaring he owned the mike and that, therefore, Bush could not tell him who to include in that New Hampshire debate.

A lot of people didn't know what Reagan was talking about. But they liked his assertion of authority. From then on he pretty much rolled on to the nomination.

That fall Reagan told Carter, ''There you go again,'' and it was enough to give him the edge in the debates, though whether he won or lost on points remained debatable. The public loves those beautifully timed and delivered jabs, particularly when they evoke laughter.

The President looked more rested than his opponent. And most polls are giving the President the nod in the ''perception'' debate. He looked better on the tube than Mondale. More than anything else, he came up with the big laugh of the evening.

Barring some unanticipated event or blunder, the outcome of this election seems pretty certain.

The President all along has had the two biggest issues of any presidential campaign going for him. The nation is at peace. And the economy is looking good.

But was Reagan too old for the job? For a long while the Mondale people wouldn't touch this question with a 10 foot pole. They were afraid that by so doing they would stir up a sympathy vote for Reagan, particularly among older people.

But in the last week or two some Democratic leaders were, at least privately, saying that Reagan's age was showing and that the public would and should be taking this into account. Then Rep. Geraldine Ferraro said it right out in the open, in response to a question.

Mondale has always thought he couldn't speak of Reagan's age. And he backed away from it in the debate. The Reagan joke was his great opportunity to come back with a humorous retort. But he didn't. In fact, Reagan had opened the door so that he could have probably gotten away with a comment about the President's age.

But, as Bill Moyers pointed out, Mondale wasn't taking advantage of openings. He was, instead, ''going for the jugular with a feather.''

Can Mondale regroup and mount a final campaign drive that will put him into contention? Perhaps.

But two things make a final come-from-behind spurt unlikely:

* Within Mondale's own camp there is dissension. It is what is called an ''open secret'' that the Mondale staff is upset with Ms. Ferraro. They think she is much too independent in deciding what she wants to do and what she doesn't. There is talk among Mondale's people that he and Ferraro aren't getting along.

Some of this may just be talk. But the fact that it is going on is reflective of an organization that is losing. It's reflective of a self-evaluation within the Mondale campaign that is anything but positive. This feeling, of itself, keeps a campaign from doing its best.

* On the President's side there is new momentum. One White House insider confides that Reagan's course now will be one of high visibility but low risk. Reagan speeches and utterances will be, as much as possible, controlled so that he doesn't come close to saying something that would damage his prospects.

One explanation for why Reagan consented to debate is that he believed his Achilles heel was his age - and that the only way to deal with it was to debate and show that he was very vigorous.

Reagan got this job done, but not easily. He faltered in the first debate, wandering and looking tired. But then he came out looking like the Gipper in the last debate. And, finally, he got that big chance that he was just waiting for: a question about whether his age would make it difficult to handle his job in an international crisis. And he leaped in and delivered the blow that destroyed the age issue - and, probably, Mondale's prospects for a comeback.