There is a note that does not ring true in the Republican convention's deliberations, chitchat and general emanations on national security, and it could yet be as upsetting in its way to those who intend to vote for Ronald Reagan as to those planning to support one of his rivals.

This disharmony lies in the tension between the call to arming, verging on a call to arms, that is the essence of the foreign policy message coming out of this convention, and the casual, lackadaisical, deceptive way in which that call is sounded.

I have in mind something that goes beyond the well-publicized fact that Reagan and his party have been unable to bring themselves to support a military draft, the classical signal and instrument of national preparedness. They have been equally unable to tell how they mean to pony up the extra scores of billions of dollars that their defense budgets will consume.

What is more disconcerting is that the Reagan people blithely refuse to acknowledge that there are inconsistencies to be explained.

The draft question is answered with a friendly bow in the direction of Reagan's libertarianism. But this ignores that Reagan, who believes in respect to the draft that the government should not be telling citizens how to lead their lives, surely has a special obligation to explain how his expensive, activist policy can be conducted without impinging on citizens' lives.

The budget question is answered with an even more grinning bow in the direction of the Reagan economic policies, as though any dunce should know that freeing up the economy will unlock all of the bountiful resources required to pay for his chosen national security policy. The logic is beautiful -- and circular.

Perhaps one should not be too demanding of a political party celebrating its certainty that the alarms for which it was condemned for rank alarmism in years past are now the stuff of the conventional wisdom. There is a sense here in Detroit that right-wing cliches have been transformed into mainstream truths and that positions that formerly needed to be argued need now only to be affirmed.

The Republicans have convinced themselves that though they held the presidency in eight of the last 12 years, the republic's unraveling has taken place strictly on Democratic time. Only the unreconstructed "hard right" spreads some of the blame to the Nixon-Ford-Kissinger period. The party is full of self-congratulation for its tough, realistic and courageous grasp of the international scene, and Jimmy Carter is its perfect foil. But only intermittently do the Republicans seem to me to be describing the real world.

Most of the time this has been a convention and party preparing for war or, better, for a mock war in which the United States will prevail without any undue suffering or loss or inconvenience.

Typically, Anne Armstrong said, without evident embarrassment, that the way to bring the American hostages home from Iran and to get Soviet troops home from Afghanistan was to send Jimmy Carter home to Plains. Loud applause.

The prevailing assumption has been that the United States will put its productive machine in high gear, outpace the Soviet Union in reasonably short order, and then face down the Kremlin by the application of a hidden American quality -- a quality hidden from Jimmy Carter, anyway: national will.

The folks here have long taxed the Democrats and the liberal left for being naive about Soviet power and excessively trustful of the Soviet Union. But the GOP has gone a long way in Detroit to enshrining an illusion of its own -- the belief that the Soviets can be faced down and that they will accept the permanent and labeled No. 2 position that so many conservatives are ready to stick on them.

Henry Kissinger dared (and it did take daring) to say that negotiation -- as well as strength and the readiness to deal with Soviet expansionism -- is an essential element of policy. But he was swimming upstream in saying that, and he had to earn a right to say it, so to speak, by backing away from his familiar call for a bipartisan foreign policy.

The Republican Party proposes to turn things around by the way, with a president who for all his Cold War conservatism seems to many to lack the sense of geopolitics -- the sense of how things connect up with each other -- that would be essential to pursuing his foreign policy goals.

What can be said about a party that claims the country faces "the most serious challenge to its survival in the two centuries of its existence," but says this while smiling prettily as though it had nary a care in the world?