Under one Pentagon estimate the nation's taxpayers will spend $50 billion over the next five years to buy more strategic weapons if a SALT II treaty is ratified and up to $80 billion if it is not.

Those figures illustrated the larger reality of the strategic arms limitation treaty SALT: the agreement can do little more than regulate the costly acceleration of the arms race already under way.

Some senators contend the price for SALT II is too high, and say much of the weaponry on the Carter administration's shopping list was put there solely to win military support for the treaty.

Other senators argue that SALT II would keep the United States from building as many weapons as it needs to achieve a strategic balance with the Soviet Union.

Neither sid e of the argument can be adjudged absolutely right or absolutely wrong because U.S. nuclear policy has gone beyond the specifics of bombs it would take to destroy the Soviet Union.

The new measure is not how much is enough actually to do that job, but how much will look like enough to everybody the United States is trying to impress. This is a judgment call - one that could pile up far more nuclear weapons for than needed to blow up al the targets on the Pentagon's list.

Former defense secretary James R. Schlesinger popularized this "perception" rationale for determining the size of the U.S. arsenal. Defense Secretary Harold Brown has embraced it.

This means that the answer to how much nuclear power is enough is like a stretch sock, it can be pulled to fit any number of sizes.

Brown, in an interview, said how much the Soviet Union spends in the future on strategic weapons - no matter if the amount is more than needed to incinerate the United States - will affect how much the United States spends for the same purposes.

"Unless the Soviets suddenly brought most of their strategic programs to a crashing halt, which a SALT II agreement doesn't force them to do, we are going to have to increase our present rate of resource allocation to strategic arms merely to keep essential equivalence" with the Soviet Union, Brown said.

"But if there is no SALT II, then I think they would do still more, and then we would do still more. In that sense, SALT II will save money. But that's not the main purpose of SALT II.

"The main purpose of SALT II, from our point of view, is to make it easier to achieve essential equivalence, to improve stability and to produce some reduction right away in some of the numbers" of strategic weapons "and to lead to still more reductions in the future."

The truth is that nobody can have a precise idea how much the United States will spend over the next five years - on the ocean-spinning missiles, bombers and other weapons that are put under the heading of "strategic forces" in Pentagon budgets.

The Pentagons's estimates of $50 billion to $80 billion, offered in response to a query by the Post, do not seem to square with the Pentagon's graphic projection in Brown's posture statement for fiscal 1980, one of which shows a sharp rise in the funding for strategic forces between now and fiscal 1984, approaching $15 billion a year even with SALT II.

Major factors pushing up strategic spending include the replacement of the Polaris and Poseidon missile submarine with the giant Trident submarine, costing $1.5 billion for the first one, and the development of the MX land-based missile.

Brown said in the interview that spending for strategic forces is likely to increase 30 to 40 percent with SALT II and 50 to 60 percent without it.

On top of the additions for strategic forces will be those for general purpose forces - the ships, planes and tanks for fighting a nonnuclears war. Here, too, the perception argument is used.

The United States and its NATO allies, President Carter and his deputies in the administration have successfully argued before Congress, must spend more for conventional forces to offset the Soviet buildup in Europe.

Otherwise, it has been argued, the Soviet Union and other nations will perceive that the United States is not serious about holding the NATO line. No leader argued that the Soviets looked more intent today than ever before on invading West Germany.

Congress has bought that argument and is expected to approve almost the entire $135 billion Carter is requesting for the Pentagon for fiscal 1980. Strategic forces represent $10.8 billion of that total.

Other pressure for higher military spending despite SALT II is coming from military leaders who argue that they must have money to buy weapons not restricted by the treaty.

One example of this action-reaction phenomenon accelerating the arms race is the Soviet Backfire bomber which is not restricted by SALT II. The bomber will be allowed to go free under certain assurances provided by the Soviets.

"What's the answer to the Backfire bomber?" asked one general rhetorically. "It's the AWACS (airborne warning and control system) and F15 no matter whether Backfire threatens NATO or the United States. We don't have to go through that argument about range."

To-build just a few of the AWACS warning planes and F15 fighters will cost the United States billions of dollars.

Similarly, SALT II allows both the United States and Soviet Union to keep spending billions of dollars to improve missile submarines and to invest additional billions on antisubmarine warfare.

Both the United States and Soviet Union are building new submarines. The Navy intends to spend billions over the next several years to replace the fleet of 41 Poseidon and Polaris missile submarines, which are wearing out.

Also, the Navy is building a new fleet of ships for the 1980s and 1990s - meaning more billions must go into the general purpose forces account to finance them.

The Army is gearing up to produce a new line of tanks - tge XM1 - as just one weapon in its multibillion modernization program that will not be restrained by SALT II.

Besides spending more money for weqpons not restrined by SALT II, there is additional spending pressure building up because military leaders believe some restrictions written into the agreement are not tight enough.

Whether the mobile MX ends up being deployed in a field of decoy missile holes or stuffed inside an airplane, this new weapon will cost between $20 billion and $40 billion - one more reason spending will go up under SALT II.

Other billions will have to go fo the cruise missile that Carter had decide to produce instead of the B1 bomber, although SALT II does limit how many can be deployed to about 3,000.

Besides the huge expenseof buying new hardware for the military over the next five years, SALT II or not, the Carter administration has publicly pledged to strive to keep the technological edge on the Soviets through intensified military research.