What is one to make of President Reagan's latest stretcher, a grave charge delivered so casually and matter-of-factly that most people, if they noticed it at all, probably let it pass as one of those characteristic overstatements to which no gracious person would expect the president to be held?

Lou Cannon and Dave Hoffman of The Post, interviewing him this week, had noted that the polls and Congress are currently opposed to financing the Nicaraguan guerrillas. Granting the point, the president explained that "we've been subjected, in this country, to a very sophisticated lobbying campaign by a totalitarian government -- the Sandinistas. There has been a disinformation program that is virtually worldwide, and we know that the Soviets and Cubans have such a disinformation network that is beyond anything we can match."

Reagan was taking his administration's fascination with disinformation -- the covert planting of forgeries or bum dope -- out of the familiar context of Third World and European vulnerability to Soviet wiles. He was suggesting, as I heard him, that in respect to Nicaragua American opinion is being manipulated: Americans aren't hearing explanations of their government's policy and some of them are returning from trips to Nicaragua with "views that are favorable to that totalitarian government."

Did the president really intend to present the dispute over the contras not as a political matter on which reasonable people can disagree -- which surely it is -- but as an instance in which the raggedy Sandinistas, even by piggybacking on hefty Havana and mighty Moscow, could have duped the American public and Congress by a successful disinformation campaign?

The disinformation theme has become a staple in an administration whose leading lights accept easily both the idea of a multi-tentacled Soviet global conspiracy and the companion notion that the American press is riddled with impressionable soft-liners and political enemies. References to disinformation adorn the statements of high officials. In the time-honored bureaucratic tribute, an interagency committee has been formed to keep track of this and other "active measures" of Soviet political warfare. The State Department regularly issues accounts of the practice; one of the latest tells of Moscow's effort to blame the United States for the assassination of Indira Gandhi.

So, you may say, exactly what is wrong with all of this? Should not the Reagan team be commended for moving into a previously untended gray area, lying somewhere between propaganda and dirty tricks, in which Soviet disinformation aggravated the chores of American policy?

Doesn't the KGB do its darnedest to use the openness of Western political systems and especially the weakness and corruptibility of Third World systems to advance Soviet interests?

Is it not a good thing for all of us to be on guard -- especially journalists, who may be the objects of manipulation and who in any event have a definite responsibility for keeping the news flow clean?

Yes, but. It is good to know what the Soviets may be up to, but it is wrong for a president to try to get out of a tight political spot by indicating that resistance to his policies arises from Soviet (or Sandinista) chicanery. To suggest, furthermore, that the struggling Sandinista regime can actually best the powerful American government, on its own turf, with "a very sophisticated lobbying campaign," indicates a strange lapse of self-confidence in an administration that otherwise insists it has restored national power and pride.

It's unreasonable too. No one has shown why better than Elizabeth Pond, who wrote a first-class series on Soviet disinformation in her newspaper, the Christian Science Monitor, Feb. 26- March 1. She laid out the record of Soviet manipulation and added something equally as valuable that the more fevered students of the practice rarely attempt: a careful judgment of the effects of disinformation in specific cases.

For example, addressing the celebrated case of Pierre-Charles Pathe, convicted as a Soviet agent of influence in France, she determined that the impact of Solzhenitsyn, d,etente and Afghanistan and other events had rubbed out whatever questionable mark on French opinion Pathe had made. Hers was a model effort to see Soviet disinformation for what it is, and only for what it is.