For almost a year, President Carter has been riding the whirlwind called the hostage issue. And now he is riding it into the final days of his reelection campaign -- either to vindication and victory or humiliation and defeat.

Among advisers to both Carter and Republican challenger Ronald Reagan, there is little doubt that the safe return of the 52 Americans from Iran before Nov. 4 -- which is both Election Day and the first anniversary of their capture -- might give the president the lift he needs to break open a very close contest.

But equally, they believe, a dashing of the public's hopes for a resolution of the hostage ordeal might be a blow from which Carter could not recover.

"There are at least as many minuses as pluses in this situation for us," said one White House aide. "And the worst of it is that we don't control the decision on which way it breaks." Even people close to the president were professing yesterday that "We're like everyone else. We're waiting to see what will happen."

While waiting, they were doing their best to discount the rumors that a deal had been made that would see the Americans leaving Iran before the middle of the week.

Across the river, at the Arlington headquarters of the Reagan campaign, there was a mixture of resignation and indignation in the talk. Aides were alternately saying that they knew all along that Carter would "pull something like this" and predicting that "the public will see how he's manipulating the situation."

From the welter of rumors and speculation about possible developments in the hostage situation and their political consequences, a few solid generalizations emerged:

Any dramatic development in the hostage story would tend to dominate the closing week of the campaign -- and probably to Carter's advantage. Except for the Tuesday night television debate between Carter and Reagan, television and newspaper coverage of politics would play second fiddle to the return of the American captives.

If Carter inserted himself into that story, by a personal announcement of their return or by leaving the campaign or perhaps the country to meet the hostages, he might enjoy a publicity bonanza that could leave Reagan grinding his teeth in frustration. That is all the more true because Reagan wants to focus voters' minds on inflation, unemployment and taxes in the final days before the election.

A successful resolution of the hostage crisis undoubtedly would make votes for Carter. There is a mass of polling data showing that attitudes toward Carter's handling of the hostages are very good predictors of voting preference. A survey by The Washington Post of eight key states, completed early this month, showed Carter enjoyed only a slight overall advantage over Reagan in dealing with Iran.

But among those who gave Carter the edge, 74 percent were prepared to vote for him, while 80 percent of those who thought Reagan would be better in that regard said they would vote for the Republican.

To the extent that undecided voters credit Carter with success in Iran, they are very likely to vote for him.

On the other hand, there is a widespread subjective view among both Republicans and Democrats that Carter is immensely vulnerable to political backlash if the latest hopes are dashed -- or even if there is something less than a prompt return of all 52 prisoners.

That vulnerability arises from the belief among both voters and politicians that Carter has been the political beneficiary of the hostage situation in the past -- and perhaps by contrivance and not just by accident.

Carter had only a 32 percent approval rating in the last Gallup Poll taken before the capture of the hostages last November. It soared to 61 percent on the wave of patriotic feelings that followed the events in Tehran and the Soviet invasion of Afghanistan. Carter used that popularity -- and the insulation the White House provided during the months he said he was too busy to campaign -- to turn back the challenge of Sen. Edward M. Kennedy (D-Mass.).

When Kennedy threatened briefly in the spring, Carter called a 7:20 a.m. news conference on the day of the Wisconsin primary to announce "a positive step" toward the release of the hostages -- a promise from Iran's president that they would be transferred from the hands of the militants to the control of the government.

Carter won with an unexpectedly wide margin in Wisconsin, but the promised transfer did not occur -- and many voters were left cynical. Later that month, the attempted helicopter rescue effort failed and, once again, the hostage issue flared.

It was not at the center of the campaign again until last week. On Sept. 13, when Ayatollah Ruhollah Khomeini set forth the terms for a negotiated release of the prisoners, Reagan said most of them seemed reasonable, and promised not to make the negotiations "a partisan issue in the campaign."

Last week, however, as reports circulated that they might be freed, Reagan said their long detention was a "humiliation and disgrace." While Reagan did not suggest that there was a political motive for the renewed diplomatic activity, both independent candidate John B. Anderson and former president Gerald R. Ford decried what Anderson called Carter's "politicizing" of the issue.

Carter and Vice President Mondale charged that it was their opponents who had brought the hostages into the campaign. But the history of the past year shows the impossibility of ever separating their fate for long from the rivalries of either American or Iranian politics.

Now that the hostage negotiations and the campaign are both reaching a climax, that linkage is stronger than ever. In the view of most politicians, if all the hostages come out this week, Carter is the favorite for reelection. Without them, his chances are dimmed.