President Reagan has based his trillion dollar defense program on the open-ended proposition that the United States must rearm until it looks strong to friend and foe alike, but more importantly that it feels strong itself.

How much money, arms and troops it will take to achieve that objective is, like beauty, in the eye of the beholder. This virtually rules out any "great debate" this year on the biggest peacetime increases in defense spending history because the majority of Congress agrees with Reagan that the United States is weaker than it should be.

Despite all the talk about systems analysts fine-tuning Pentagon budgets down to the last bullet, the record shows that "how much is not enough" has been a subjective question -- a political, if not emotional, judgment -- at least since the Eisenhower era when the United States enjoyed undisputed nuclear superiority over the Soviet Union.

The result has been that decision makers at various times have proclaimed radically different military goals for the nation without radically changing the size of the force to carry it out.

Moreover, the subjective basis of determining how much is necessary for military strength explains why the size of the annual defense budget in peacetime has depended as much on each president's sense of the national mood as on the external threats to the security of the United States.

President Kennedy set out as the 1960s opened to counter wars of liberation. His defense secretary, Robert S. McNamara, said the goal was to raise enough forces to fight two big wars and one little one at once -- the 2 1/2 war strategy.

President Nixon, believing Vietnam had painfully demonstrated that one big war and one little one such as in Indochina was about all the U..S. military could handle, scaled down his rhetoric accordingly -- proclaiming a 1 1/2 war strategy. His defense secretary, Melvin R. Laird, made no secret of the fact that this nation's political mood -- which had nothing to do with any military threat to the United States -- helped decide how much is enough.

Laird said on Feb. 20, 1970, as the Vietnam war seemed to be winding down, that certain conditions dictated sharp reductions in the Pentagon's fiscal 1971 budget: "The determination of President Nixon to reorder our allocation of federal resources to bring them in line with changing national priorities; the crucial need to bring inflation under control and the president's dedication to this objective, and the clear intent of Congress to make major reductions in defense spending."

Suddenly, because of economic and political conditions in the United States, what the Soviets, Chinese and guerrillas around the globe were doing did not seem as menacing as inflation and sentiment in the House and Senate. Looking from the domestic end of the telescope then at a world picture that is not drastically different from the one that exists today, Laird concluded in that 1970 posture statement:

"The Soviets are continuing the rapid deployment of major strategic offensive weapons systems at a rate that could, by the mid-1970s, place us in a second-rate strategic position with regard to the future security of the Free World." But in the next paragraph he held out high hopes that arms negotiations, rather than an arms race, would take care of that problem, declaring:

"The Soviet Union has agreed to discuss the limitation of strategic weapons systems with us in Vienna beginning in April. Hopefully, success in the strategic arms limitation talks (SALT) will move both our nations along the road toward the era of uninterrupted peace we all seek. The dividends for our domestic programs could thereby be increased still further."

Similarly, as another part of this justification for favoring butter over guns, Laird gave a view of the world that could be repeated today if one chose to be optimistic:

"As the president noted, the world has changed significantly during the past two decades. We now have stronger allies with sounder economies; a less cohesive Communist world now exists, and many more nations are developing independently. As we look to the future, we must carefully define our national interests with special concern for the legitimate interests of other nations, while recognizing that deep-seated differences among nations will continue."

In the 11 years since Laird spoke, most allied economies have continued to maintain greater overall strength than those of the Warsaw Pact; China and the Soviet Union have continued to drift apart, and the drive for independence in the Third World has accelerated.

True, the Soviets have kept increasing military spending year after year while this nation's zig-zagged. As former defense secretary Harold Brown stressed repeatedly to Congress, the Soviets chose to move steadily along like a tortoise while the United States progressed like a hare, in fits and starts, raising the Pentagon budget one year and cutting it the next.

Also, since Laird spoke, Washington has become increasingly alarmed about threats to foreign oil supplies. However, the fact is that Soviet troops have not moved against Saudi Arabia or Nigeria, the two biggest suppliers of U.S. imported oil, nor jumped across the border into turbulent Iran.

For now, President Reagan and his secretary of defense, Caspar W. Weinberger, are rushing ahead with weaponry they think will make the country feel and look strong in a world they and Congress see as more dangerous than ever. The willingness to drag old battleships out of mothballs and send them charging into foreign waters dramatizes the emotionalism that will propel Reagan's record high peacetime defense budgets through Congress. The critics who try to get more bang for these bucks or question whether they are excessive are not expected to have much of a year in 1981.

Chairman James R. Jones (D-Okla,) of the House Budget Committee was asked if the defense juggernaut is apt to be slowed this year by politicians worried about spending so much on arms at a time the national economy is sick:

"I don't think that's realistic," he said.