Without so much as a drum roll, Congress is about to launch the American military's biggest peacetime buildup.

The congressional approval will take the form of budget ceilings established for national defense for the next three years -- fiscal 1981 through 1983. While the Senate and House are currently at odds over whose budget numbers to adopt, the Senate Budget Committee reckons that its higher objectives for defense spending would total about $1 trillion over the next five years.

A trillion dollars -- that's $1 with 12 zeroes after it. A trillion dollars sounds extraordinary, but the unspoken fact of this new defense buildup is that it will not make the United States the undisputed No. 1 in global military might.

In fact, assuming continued peace, the armed services will eat up that trillion dollars without growing much bigger than they are today. Five years from now, critics still will be able to deplore the various "gaps" between the U.S. and Soviet military -- the tank gap and the naval gap and the fighter plane gap and the nuclear megatonnage gap.

The Army, under the Pentagon's blueprint, will not be significantly bigger in 1985 than it is today -- about 776,000 officers and soldiers. Although there has been a lot of talk about President Carter's Rapid Deployment Force for the Indian Ocean and other hot spots, the RDF will be made up of existing military units, not additional ones.

A big slice of that trillion will buy new armor for the Army -- including nearly 3,800 more tanks. But there will still be a tank gap with the Soviet Union in 1985.

Navy admirals insist they need a 600-ship fleet to cover the world. The Navy's big slice of the trillion will buy some new ships, but not enough to reach that goal. The 1985 outlook for naval aviation is more grim -- fewer planes five years from now than today, as losses outstrip purchases.

The Air Force long has been pushing for a new bomber and new land-based missile, the MX. The bomber will get more study, and perhaps some started. But neither will be deployed by 1985 under current planning.

Marine Corps leaders deplore the lack of planes and ships to transport their troops quickly to distant trouble spots. But their share of the trillion dollars will not buy all the "lift" they think they need.

How can the president and Congress go on a five-year shopping spree which is going to buy so much frustration? The answer lies in the complexity of modern weapons and the uncontrollable costs of maintaining military forces:

Only about one-fourth of the Pentagon's total budget goes to buy weapons -- the procurement account. The rest goes to pay, house and feed the armed forces, to maintain weapons on hand, and to conduct research on promising wonder weapons.

The $250 billion which under normal apportionment will go for procurement over the next five years -- assuming the Senate's projections prove accurate -- does not seem to buy as much because the modern weapons cost so much more than the old ones they replace.

World War II's famous Sherman tank cost $70,000 a copy, but the Army's new XM1 main battle tank costs $1 million each. The World War II Essex class aircraft carrier cost $43.7 million; today's nuclear-powered Nimitz, $2 billion. The P51 fighter plane of World War II could be built for $51,000; today's F15 fighter, $29 million.

Inflation accounts for some of this price escalation, but only a minor part. A Sherman tank would cost only about $235,000 in today's inflated dollars, still vastly cheaper than the XM1 tanks the Army will buy.

Pentagon executives attribute much of the difference to quality. Critics call it gold-plating. But post-World War II does show that U.S. decision-makers have consistently opted for high-technology, sophisticated weaponry instead of simpler, cheaper and sometimes more reliable versions. The Americans favor Cadillacs and fancy vans; the Russians build Chevvies and plain old trucks.

When Pentagon civilians try to switch toward simpler and cheaper weapons or to consolidate several functions into one weapons system, they often run into stiff resistance within the armed services and are usually overruled by Congress. Past fights to switch to smaller and cheaper aircraft carriers and submarines ended in failure.

Much of the U.S. arsenal was lost or worn out during the long Vietnam war. So a big chunk of the $250 billion for procurement will be spent simply to replace what was lost or is now obsolete. A vast modernization program is under way, one that does not show the United States catching up to the Russians under the usual comparisons.

The Soviet Union shows no sign of slowing its own steady, relentless buildup in weaponry across the board. Pentagon leaders believe, however, that the U.S. economy can handle heavier defense spending more easily than the Soviets can, so they predict that we will eventually gain on the Russians if we stick to the accelerated pace.

Will citizens begin to ask why their tax dollars seem to be buying so little strength in relation to the Soviet Union? Some Pentagon leaders already argue that the usual "we" vs. "they" comparisons in troops, tanks and megatonnage do not explain the true relative strength of the two superpowers.

Defense Secretary Harold Brown, in his fiscal 1980 posture statement, insisted that such comparisons "can be extraordinarily misleading when it comes to making judgments about the adequancy of our forces or how to correct their deficiencies.

"While we would be fighting alongside allies in most cases, the comparisons frequently omit their forces. They also leave out such crucial variables as objectives, geography and contingencies. The impression they give is that the United States and Soviet Union are going to meet on a jousting field, where they will engage in a fight to the finish with all their bombs, bullets, tanks ships and aircraft -- possibly with allies, but more likely without them.

"Since there is a strong propensity to compare like systems, tanks with tanks and destroyers with destroyers, the comparisons are likely to overlook such considerations by NATO to counter Soviet tanks with antitank weapons or the effort by the United States in many areas -- perhaps mistakenly -- to reduce the quantity of its weapons to buy individual weapons of very high quality -- and cost."

Brown warned: "These comparisons can also lead to the conclusion that the way to improve or restore our posture is to make its details a mirror-image of Soviet capabilities. That would be a mistake."

Yet such appeals have been under-cut by the president's own policy statements, starting with a reversal of his own 1976 campaign promise to cut defense spending $5 billion to $7 billion a year. In 1978, President Carter convened a NATO "summit" conference in Washington where, under his prodding, the United States and its allies promised to increase defense spending by 3 percent a year, after allowing for inflation.

Carter's new blueprint for fiscal 1981 to 1985 calls for an after-inflation annual growth averaging 4.6 percent in money that can be obligated and 4.1 percent in spending.

Sen. William Proxmire (D-Wis.) is among the critics who insist that -- instead of setting a fixed percentage growth rate for defense spending -- the Pentagon budget should be justified in specific terms: how much is enough and why. "It's ridiculous," said Proxmire.

"Imagine what they'd say if we did that on domestic programs."

However, the administration and Congress apparently are in step with the voters who want to spend more money on defense to catch up to what they perceive as a Soviet lead. A Washington Post poll suggested the public believes No. 1 is the Soviet Union, not the United States.

A Post survey in April posed this question:

"Which nation, the United States or Russia, do you think is stronger militarily right now, or is that something you haven't formed an opinion on?"

By 2 to 1, Americans feel the Soviet Union is now stronger.

What will America get for the money? Here are the big-ticket items to be financed according to Carter's five-year plan:

MX land missile. After getting more than $3 billion for research and military construction in 1981 and 1982, the MX blockbuster missile is scheduled to received $10.2 billion in procurement money from fiscal 1983 through 1985. The MX would get $4.9 billion in 1985 alone, as missile production rose from 18 in 1983 to 71 in 1985.

Counting everything, the Pentagon has said the MX will cost about $34 billion but the General Accounting Office predicts a much higher price tag -- $57 billion. This would buy 200 missile for deployment and 30 for spares to supplement the land-based missile force of 1,000 Minuteman and 34 Titan ICBMs.

Cruise missiles. Carter, in his most important decision on strategic forces, chose cruise missiles over the B1 manned bomber. The cruise missile is a pilotless drone launched from an airplane or ground platform. The weapon's mechanical brains follow a terrain map and guide the nuclear warhead directly to the preprogrammed target.

Carter proposes to spend $2.6 billion to buy 2,400 air-launched cruise missiles from 1981 through 1985. He has earmarked an additional $1.4 billion to buy 425 groundlaunched cruise missiles.

Army tanks. Although the Army hopes the cost of its new XMI main battle tank will work out to no more than $1 million a copy, the price will not start declining until savings start from mass production. Carter has earmarked $6.2 billion for 3,800 tanks over the next five years.

If the Pentagon tried to close its tank gap with the Soviets -- roughly 10,000 vs. 45,000 -- by purchasing 35,000 XM1s at $1 million each, that alone would cost $35 billion. This would take up almost the entire Army fiscal 1981 budget of $39.8 billion -- a goal sophisticated armored personnel carrier, in the five-year period. That money would buy 3,703 of these vehicles.

Navy ships. Carter's five-year plan calls for buying 97 new ships and converting five others. Warships on his shopping list include six Trident missle submarines, five Los Angeles-class attack submarines, six fast-attack submarines still on the drawing board; 16 guided-missile destroyers; 15 patrol frigates, and 14 cargo ships for the Rapid Deployment Force.

All told, Carter proposes to spend $45.2 billion from fiscal 1981 through 1985 to build up the fleet. But even this money -- roughly equal to the entire Pentagon budget of 1962 -- will not be enough to buy the 600-ship Navy the admirals want.

For example, today's Polaris and Poseidon nuclear missile submarines are wearing out faster than Tridents can be built to replace them. The Navy already acknowledges there will be a gap between today's and tomorrow's sea-based deterrent as a result. Some surface ships will experience the same kind of lag because of the retirement of old vessels.

Defense Secretary Brown predicts the fleet will grow from 535 ships today "to about 575" by 1985. The House Armed Services Committee is among the skeptics who doubt that Carter's five-year plan will produce that many ships. The committee has recommended raising Carter's fiscal 1981 ship-building account from $6.2 billion to $8.4 billion, for openers, "to reach and sustain a force level of about 550" ships.

Aircraft. The Air Force from 1981 through 1985 would receive $51.3 billion and the Navy $37.2 billion for new aircraft.

Of the Air Force total about $8.5 billion would go for F16 fighters, $2.5 billion for the F15 and $1.8 billion for the A10. The Navy's aircraft procurement account earmarks about $2.5 billion for 66 F14s and $13.5 billion for 656 F18s. But, after spending all that money, the Navy acknowledges it probably will have fewer fighter planes in its inventory than it does today.

Here why: The Navy should buy between 160 and 200 aircraft a year simply to replace those that wear out or crash, principally fighters, according to congressional calculation. But the total buy of 722 F14s and F18s, stretched over five years, means the Navy will get about 145 new planes a year -- not enough to keep ahead of losses.

The Navy buys so few planes each year because of their high price tag. Yet if fewer planes are purchased, that means more overhead for the manufacturer per unit of production -- pushing up the price even higher.

While inflation contributes to higher prices on weapons, a look at the Pengagon's shopping list in the 152-page book, "Program Acquisition Costs by Weapon System," dramatizes the Pentagon's insistence on quality over quantity -- technological sophistiication that costs a lot more.

Here is a sampling of price tags for fiscal 1981 from that Pentagon book -- price tags arrived at by dividing the number of weapons into the procurement dollars (the prices sow include spare parts, but not research costs):

Army Blackhawk troop helicopter, $4.2 million. Army should-fired Stinger antiaircraft missile, $52,000. Navy Trident submarine missile, $12 million. Navy F18 fighter, $34 million.

Air Force F15 fighter, $29 million. Air Force and Navy Sidewinder heatseeking air-to-air missile for dog-fighting, $175,000. Air Force and Navy Sparrow radar-guided air-to-air missile, $130,000. Marine 155-millimeter howitzer, $312,000.

A Pentagon leader worries aloud about the danger of buying weapons so expensive that the services can't afford to train the troops on them.

But, in the absence of a meaningful arms control agreement with the Soviets or a vastly different approach to weapons buying the Pentagon will continue to look like a man running faster to stay in place.