Dear "friend," the letter said, send money: "$1,000 or $100, or $25, whatever you can afford. . . . Join us in our fight to bring some sanity to our confused and hostile cultural climate." It was signed by Midge Decter, in her capacity as executive director of the Committee for the Free World. That's a blue-ribbon, right- wing, international organization whose American members of the board include such leading neo-conservatives as Irving Kristol and Norman Podhoretz, U.N. Ambassador Jeane Kirkpatrick (on leave) and columnist George F. Will.

Now the message: the typical American loves his country and wants it to be a great world power, but our leaders have lost confidence in themselves, Republicans as well as Democrats. This is because wicked opinion makers in the media, the universities, the arts and the churches, have been spreading "false and dangerous" notions that American society is "unjust"; that American policy favors "tyranny" while Marxist-Leninist revolutions are on the side of "good."

Nothing else can explain why there is growing support for a nuclear freeze and for cutting the defense budget, when as "recently as 1980 the voters of America delivered a resounding mandate for the renewal of American power." The people couldn't be that "fickle;" the trouble is they are "confused."

Well, that could be. But another explanation for much of what's anguishing Decter and her conservative cohort is available in a new study by the Chicago Council on Foreign Relations entitled "American Public Opinion and U.S. Foreign Policy 1983." It is based on an exhaustive poll by the Gallup Organization that compares the thinking of the American public at large (and a smaller sampling of American leaders) with its thinking four years ago on a broad range of issues: defense needs; the U.S. role in the world; national priorities; the most serious threats to U.S. security.

Its inescapable conclusion is that the Reagan foreign policy mandate was never as "resounding" as his followers claimed. Between 1974 (when the council did the same study) and 1978, preoccupation with a "perceived growing military imbalance between the United States and the Soviet Union" increased markedly. The council's analysis of the Gallup findings acknowledges the Reagan administration has eased the public sense of military insecurity by its "unprecedented peacetime increases in military spending."

But the ironic consequence is that today more people want to cut back defense spending than want to increase it --the exact reverse of four years ago. Some 42 percent see the United States and the Soviets as military equals and 21 percent think the United States is actually stronger.

In just about every other respect, the council reports, "the foreign policy attitudes of the American republic have maintained a basic stability" that is "all the more surprising" given the election of a president who "pledged to set the nation on a new path in foreign as well as domestic policy."

So the Committee for the Free World is right: people are not all that "fickle." But that doesn't mean they are faithful to the Reagan foreign policy approach. The point is that (aside from defense spending) the latest survey shows roughly the same reservations and ambivalence about foreign policy that existed four years ago.

Domestic issues lead the list of priorities. Americans are somewhat more willing than they used to be to commit American troops overseas under certain conditions, but a clear majority is opposed to giving or even selling arms to foreign friends and allies.

Summing up, the council report finds in the latest survey "a continuing erosion of the post-World War II public consensus that the national interest requires active participation by the United States in world affairs. Only a bare majority of the public now holds the opinion that such international activism is best for the future of the country."

Decter notwithstanding, the "leaders" sampled in the Gallup survey (including Reagan administration officials as well as a bipartisan collection of politicians, businessmen, editors and publishers and television broadcasters, scholars and churchmen) showed themselves more eager than the public for an active U.S. role in the world. But they are also less likely to see a communist threat in "peripheral areas."

So the conservatives of the Committee for the Free World may find some corroboration of their "confusion" theory in the Chicago council's report. But that only leaves you wondering who's been holding the high ground for the past two years--the Great Communicator leading a supposedly conservative Reagan administration, or some gaggle of opinion- makers deliberately setting out to "sow confusion." You have to ask yourself this, as well: whatever happened to that "resounding mandate"?