FOR PLAIN folks, sending a telegram overseas usually costs about a dollar or two. But last week Washington spent $1.5 billion on a message to our allies and the Soviets. By okaying funds for the controversial MX missile and thereby ending years of rancorous debate, Congress showed for all the world its readiness to back President Reagan's peace through strength rhetoric with action.

Last Tuesday's episode on Capitol Hill was yet another demonstration of one of the major paradoxes in modern times: the need for the countries of the free world to spend hundreds of billions of dollars annually on deathly weapons just to keep the peace. But the inescapable fact that much of the national budget must go to defense does not mean that the money should be spend indiscriminately. A commitment to national security does not relieve decision makers of the burden of choice when it comes to means.

What was so disturbing, then, about the MX vote was the Reagan Administration's success in persuading a majority of lawmakers to pursue the goal of a strong defense blindly. The faults of this particular multiple warhead system are many and well-documented, chief among them being its vulnerability to a knock out strike. But the President made clear through his no-holds-barred lobbying effort that he was less concerned with the quality of the system deployed than just deploying something to demonstrate firmness to Moscow and its Geneva delegation. Similarly, a refusal to undermine our negotiators at arms talks led congressmen to vote in favor of the MX as symbolic of our commitment to peace. Perhaps less expensive symbolism and more stable missile would help the cause of national security.

But the really tragic part of the MX debate was that the one quarter of the House Democrats who crossed party lines to vote to the weapons, without whom the effort would have failed, did so out of fear that the Republicans would get a lot of political mileage out of labelling them soft on defense. Political calculations held reasoned judgement hostage.

DRAWING ANALOGIES from history is risky business, but nevertheless there was something about the MX battle unmistakably reminiscent of the early days of Vietnam. In debating the correctness of our involvement there, successive Administration managed nearly to ignore the actual situation in that complicated little country where the odds were heavily stacked against a successful U.S. intervention. Insisted on using Vietnam as an arena in which to demonstrate to friend and foe alike our readiness to resist communism anywhere and everywhere in the world. In addition, foreign servicemen, bureaucrats and lawmakers all backed this position not for its merits, which were few, our of concern lest they be branded soft on communism. Likewise, last week's issue wasn't about the MX but about resolve--and those key congressmen who voted in favor cared more about looking tough in this day of renascent machismo than about acting wisely.

An off-overlooked aspect of the Vietnam years was that the Johns Administration's refusal to raise taxes in order to finance its war effort ultimately triggered years of inflation and economic havoc. Should the current Administration's thriftless policies lead to economic crisis public opinion will surely turn against arms programs and Congressman will regret having shot their expensive wad on a marginally effective bunch of missiles at the expense of some future sound and necessary system. If there is a lesson to be learned from Vietnam, it is that when government take the right stand in the wrong place they can only ultimately discredit a valid position.

In these next couple of years the country will witness similar battles about defense issues or, congressional floors as the conflicts between administration's rearmament dreams and budgetary realities come to a head. The White House's proposal for a 6 percent real increase in the defense budget, already the source of heated congressional debate, pales in comparison to its plans for 8 and 9 percent growth for the military in 1986 and 98."

Congressmen will fail in their crucial duty to separate the wheat from the chaff in these Pentagon dreambooks if every time they attempt to bring the Administration back to earth their political opponents brand them doves. The again, they might grow tired of the Administration's claim that only a sky's-the-limit missiles buildup budget can effectively communicate our seriousness to the Soviets and become bearish on defense. Either way, the country is not likely to get the affordable national security we need, which is just what happens when reason tails to govern.