A debate is a debate and a news panel is a news panel; never the twain should meet has been my view. But the way the slanging match on foreign policy has been going in recent days, the news panelists may be the electorate's last, best hope for keeping the Kansas City foreign-policy contest honest.

One example illustrates the point: the recent, rancid wrangle over the administration's record in Lebanon. True, there is much more to this year's foreign-policy debate. But much of it has to do with unfinished chapters: arms control, U.S.-Soviet relations, Central America, the Atlantic Alliance.

Lebanon, however, is an across-the- board test of a regional policy; of the management of military force; of the practical application of "deterrence"; of a geopolitical world view. Those were the stakes Reagan piled upon the presence of the U.S. Marines as a part of a multinational peacekeeping mission. Lebanon is a story with a beginning (the initial deployment of the Marines) and an end (their abrupt withdrawal).

So Lebanon would deserve extensive airing in Kansas City even if the issue had not been already knocked far beyond the bounds of fair comment by Vice President George Bush's allegation that both Walter Mondale and his running mate have been saying our Marines "died in shame" in Lebanon.

Later, when challenged, Bush produced a quotation from Mondale -- "once again we're humiliated in the region" -- and a dictionary (American Heritage) defining humiliation as the same thing as "shame." He also had a quote from Geraldine Ferraro that "250 young men died in a mission without a purpose and for a policy that's never been explained." Bush said that accusing young men of "dying without a purpose and for no purpose is, in the lexicon of the American people, a shame."

First things first: To suggest that either candidate was saying -- or that anybody would say -- that American servicemen had "died in shame" in Lebanon is in itself to dishonor their sacrifice. The humiliated "we" that Mondale had in mind was the United States. If you don't think that U.S. prestige and influence suffered humiliation in Lebanon, you have only to ask America's friends in the region.

Ferraro may have been a bit off the mark in her reference to a "policy that's never been explained." The administration's problem is that its policy was explained and re-explained. In the process, its purpose expanded beyond anything that so modest, and mismanaged, an application of American power could hope to achieve.

If Reagan is to defend his Lebanese policy, he must explain how the initial Marine deployment to help remove the PLO fighting forces from Beirut evolved into re-deployment to stabilize Lebanon's government. Later, Reagan was to say that Lebanon's stability "is central to our credibility on a global scale." At other times he spoke of Lebanon's crucial connection to the security of Persian Gulf oil and the struggle against communist conquest of the Mideast.

Finally, he was saying that Syria was "bent on territorial conquest" in Lebanon and that "they want to drive us out because they can't recognize their territorial ambitions as long as we are there . . . . If we get out that means the end of Lebanon. And if we get out, it also means the end of any ability on our part to bring about an overall peace in the Middle East. And I would have to say that it means a pretty disastrous result for us worldwide." That was in a Wall Street Journal interview on Feb. 3. Three weeks later we were "out."

Now that strikes me as humiliation as defined by my dictionary (Webster's) -- to "hurt the pride or dignity of by causing to be or seem foolish or contemptible." By that same dictionary's definition, "a person who tries to stir up people by appeals to emotion, prejudice, etc., in order to win them over quickly and so gain power" is a "demagogue." And that does not strike me as too strong a word to describe anybody who could take those citations from Mondale and Ferraro and twist them into a suggestion that American Marines in Lebanon "died in shame."