One reason a number of government analysts do not share President Reagan's view that the Soviet Union now has strategic military superiority over the United States is that the Russians, as one official put it recently, "are always catching up to us."

What he meant, and what the Pentagon's new book on "Soviet Military Power" documents, ironically, is that Moscow's prodigious military design bureaus and production ministries are the world's leading copycats.

From space shuttles to antitank rockets, from C5 transports to Airborne Warning and Control Systems (AWACS) radar planes, the Soviets put into production weapons the United States conceived of and produced first.

Pointing this out is not to downplay the awesome military power of the Soviet Union. And by copying American weapons and concepts, by buying or stealing American technology, the Soviets save time and money and avoid the uncertainty of whether something will work.

But what does this say about Soviet inventiveness and, ultimately, Soviet military self-confidence? What it may say is that, when the chips are down, the Soviets could come out second best in a battle because the West will always be one step ahead or will have that one piece of equipment in service that the Soviets will not have yet.

It would be wrong to overstate the implications of the recent success of Israeli forces, equipped with American weapons and some of their own, against Russian-built planes, tanks and air defense missiles in Lebanon. That Soviet equipment was operated by Syrians. It is not the very best that Moscow has to offer, was not present in the vast quantities that the Soviets have in their own arsenal, and was attacked by one of the world's sharpest air forces. Nevertheless, the Israeli operation showed that western technological and tactical ingenuity can overwhelm front-line Soviet equipment.

Similarly, the Pentagon's new book reports that the Soviets are using some of their newest equipment in Afghanistan. But they have not been able to take real control of that country or defeat the rebels.

There is some on-the-record indication that the Soviets fear they are second-rate thinkers when it comes to modern weapons. A year ago, a pamphlet called "Always Ready to Defend the Fatherland" was published by the chief of staff of the Soviet armed forces, Marshal Nikolai V. Ogarkov, who pointed out that the United States was the producer of the breakthrough weapons, from atom and hydrogen bombs to nuclear-powered submarines and multiple-warhead missiles.

There is also some indication that the late Soviet leader Leonid I. Brezhnev, in his final message to the military hierarchy last October, had such concerns in mind when he warned that "competition in military technology has sharply intensified, often taking on a fundamentally new character. A lag in this competition is inadmissible."

If Soviet self-confidence is at issue, it may also be worth asking how reliable are those Soviet weapons that are largely copies of others' brainchildren.

The Pentagon's new booklet portrays Soviet weaponry in largely breathless and uncritical terms; at times it reads like a manufacturer's brochure. Every new model of weapon is "significant" or "impressive" or will "enhance" or "substantially increase" the threat. Readers are told, for example, that a new version of the Russian Fencer jet fighter-bomber "with its all-weather, low-altitude penetration capability manifestly increases Soviet ability to carry out deep strikes into NATO territory with little advance warning."

Is our government certain of that? Will all those expensive all-weather F15 fighters this government has sent to Europe in recent years be to no avail while the Fencers are streaking to their targets? And how will a fighter-bomber arrive with little advance warning if the new U.S. AWACS planes are working?

What we do know is that the Soviets' new intercontinental ballistic missile failed in its first test last October and that intelligence sources report that Moscow's newest submarine-launched missile has also experienced test failures. Soviet submarines in recent years have suffered some embarrassing incidents at sea, either going dead in the water or running aground, and there were reports of a mutiny on a frigate.

The Russians, like the Americans, will fix their weapons and more or less make them work. But they probably have as much of a problem with their weapons' reliability as we do with ours, maybe even more if the mindset that goes with so much copying also afflicts their production processes.

What the Soviets excel at is quantity. They have a massive army and 42,500 tanks in Europe alone. They produce 2,000 new tanks annually, some 53,000 surface-to-air missiles and seemingly thousands of everything else, according to the Pentagon report. The sheer quantity of these conventional forces is what seems menacing, just as the size of Moscow's intercontinental missile force in terms of what it might do to American missiles if Moscow struck first.

What "Soviet Military Power" also conveys is the sense of a military establishment that has been allowed to run amok, at great cost to the rest of Soviet society. No matter what it is, the Soviets seem to build it.

A big four-color drawing of a new anti-ballistic missile radar--"part of the continuing modernization of Soviet military power"--opens the Pentagon report. Not surprisingly, the radar looks just like one we built 10 years ago and then junked because scientists do not believe an antimissile system will work and because radars such as these make excellent and easy targets.

In contrast to the first version of this Pentagon report, published in 1981, the latest edition does include some comparisons with American forces that add some balance. And at the end of the report, Defense Secretary Caspar W. Weinberger says that all this Russian power should not "provide the slightest basis for despair" because the Reagan administration is rebuilding U.S. strength.

Nevertheless, the overwhelming tone of the book is that the Russians are coming and we are going to be on the short end. While this may help win votes for the defense budget, it can also be depressing and misleading.

Whatever the numbers show, the U.S. Air Force and Navy are judged as superior to their Soviet counterparts and no American military leaders are inclined to swap forces and equipment with the Russians. Similarly, the U.S. military would not want to swap allies. The Soviet Union is ringed by Communist China and potentially unreliable allies in Europe, such as Poland. The United States has allies in England, West Germany, and France with potent military capabilities.

The Soviet navy faces potentially enormous geographical disadvantages in wartime and can much more easily be bottled up in its home ports than can Allied fleets. The Soviet army is not without problems of alcoholism and ethnic rivalries.

Soviet nuclear missile power is very real and very threatening. But so is this country's. The overall national intelligence estimate is that a rough strategic parity still exists between the two superpowers, according to government sources. Each side has the power to deter, neither to overcome.