IN PUBLIC OPINION polls conducted and released since the Detroit convention, Ronald Reagan leads President Carter by as much as 28 percentage points. In a presidential campaign, one percentage point is believed to represent more than 800,000 individual voters. So, if you wanted to be really discouraging to your friend with the Carter-Mondale bumper sticker, you could point out that 28 percentage points means that Mr. Reagan is leading by about 22.5 million votes.

But as all candidates know, polls change, and today's overwhelming favorite can become November's also-ran. Politics can be a cruel enterprise, something of which the members of the Siro Agnew Presidential Library Committee do not have to be reminded.

But the problem of handling The Bad Poll remains, and is likely to get more attention this very week. So how can candidates and their official spokesmen answer the inevitable calls after the bad poll?

There are different schools of thought on this:

1) The No Guts/No Glory School.

Ideally, the campaign spokesman using this response should be able simultaneously to swagger and talk semi-coherently with a lighted Lucky Strike in the corner of the mouth: "Hey, if Christopher Columbus had taken a poll, your family would still be planting potatoes and this election would be for the tribal council." A variation can be used for non-Columbus fans: "Thank the Lord that Winston Churchill didn't have George Gallup's (or Lou Harris') phone number in 1940. Any poll would have told Churchill that the Battle of Britain was a loser, that the Germans were sure winners. And that poll would have been wrong, too."

2) Offense Is The Best Defense School.

The person using this tack should be someone who looks at least not uncomfortable with a computer printout. What he does is attack the source rather than the substance of the information.

"As anyone can tell you who has had anything to do with elective politics, there is only one word to describe this year and this electorate; volatile. We did not make it this far by developing a strategy for a static electorate, believe me.

"But even more important is the fact that this election is not one national poll like the one in the papers. No, this election is 50 separate statewide 'polls.' And there is only one poll that counts, and our opponent knows it, too, and that is the poll on the first Tuesday after the first Monday in November.

"And finally, the sample used in the poll was faulty, the questionnaire was amateur and the telephone is notoriously unreliable at this stage of a campaign."

3). The Grizzled Veteran Approach.

This method is preferred by the older spokesman who has been politically active longer than the reporter has been out of junior high school. The spokesman affects the air of someone who has seen everything, including the Dallas Fair, twice: "Do you remember President Dewey or President Muskie? No, that's unfair, you are too young. But these very same pollsters had both of those men giving their inaugurals.

"Look, kid, I want to save you some embarrassment. This poll was done by the same people who predicted that "Supertrain" would be the biggest hit on television. Okay? And, of course, you don't have to be reminded that there was a young man from Georgia whom no one had ever heard of until he won, and only then did the pollsters even bother to list him."

Now, of course, everyone's heard of him -- and the polls are getting worse . . .