HOW THE OTHER HALF LIVES : THE NEW RUSSIANS <i> By Hedrick Smith (Random House: $24.95; 621 pp.) </i> : THE HIDDEN NATIONS The People Challenge the Soviet Union <i> By Nadia Diuk and Adrian Karatnycky (William Morrow: $24.95; 352 pp.) </i>

Hedrick Smith produced the most informed and devastating popular expose of the Soviet system that had yet been written; his “The Russians” was the fruit of three years in Moscow between 1971 and 1974, during the stagnant Brezhnev era. In sections entitled “The People” or “The System,” he wrote about a society that seemed as static as a museum artifact.

Now, in his magisterial “The New Russians,” such an approach no longer is possible. The Soviet Union is so beset by political change and uncertainty that most books attempting to describe or predict it are obsolete almost before publication. Smith’s chapters, tellingly, now are titled “The Awakening” or “The Empire Tearing Apart” or “The Taste for Democracy,” and his book reads more like a history of the last five years than a social inquiry.

“The New Russians” is rich in experience and huge in scope. It charts a kaleidoscope of different movements and beliefs, and ranges from the early roots of Soviet reform to a cautious prognosis for the future. In particular, Smith’s comprehensive picture of the workings of Soviet power politics during the past half-decade is shaped by an incipient understanding of the divergent roots and allegiances of its players.

This political narrative is enriched by studies of Soviet life where perestroika has changed or challenged it: the tentative emergence of free enterprise, the flowering of a semi-independent media, the emergence of public protest--all set against the stubborn stagnation of industry and agriculture. And his survey is bolstered by a host of biting interviews--mostly with political and civic leaders--given over the course of nine months of intermittent travel.

One man, of course, stands center-stage, and Smith’s biography and analysis of Mikhail Gorbachev--of the president’s motives and capacities--are conventional but unusually full and convincing. He describes a man of high pragmatic intelligence who set out with the objective of cleansing and reforming the system rather than replacing it. We are left with the picture of a still buoyant but embattled strategist, endlessly adapting to the torrent of needs and fears that he has released. Especially interesting are the early influences on Gorbachev’s thinking and the provincial upbringing which left him so ill-equipped to anticipate the mood of the non-Russian republics in the U.S.S.R.

The book analyzes four of these divergent republics--Uzbekistan, Armenia, Azerbaijan and Lithuania, Its blow-by-blow account of the Baltic drive for independence is grimly readable, So is its portrayal of the Armenian-Azerbaijan conflict. In both cases it is inevitable that a story that already is somewhat out of date will be pure history within a year; but this accurate and lucid narrative supplies order and perspective to a drama usually transmitted only through the piecemeal servings of journalism.

As for Gorbachev, “he might not have understood the power of nationalism in the minority republics,” Smith writes, “but as a Russian, he understood that nationalism had a powerful pull on his own discontented people, who were looking for someone to blame and something new to believe in.” The upsurge of Russian ethnic feeling, and the unlikely alliance between its reactionary protagonists and the Russian democrats of Yeltsin, make for one of the most arresting chapters in the book. Everywhere, the overall “Soviet” power dwindles before the emergence of ethnic passions.

But the root of this book’s strength lies above all in its understanding of the Russians’ psyche: their fear of the chaos lurking in anything new; the distrust of their own inner anarchy; the need for belief, and the timeless expectation that the state will supply it, “History has not taught the Russians the habit of compromise or restraint,” Smith writes. “Theirs has been a winner-take-all politics. And so they have a gut anxiety that others will use freedom against them; they find it hard to trust each other to use it responsibly. So to a greater extent than Westerners, Russians have been relieved when order was imposed on them; and in the great mass of Russians, authoritarianism has bred passivity.”

In his prologue, Smith sees the present Soviet turmoil as a “modern enactment of one of the archetypal stories of human existence, that of the struggle from darkness to light . . . “ To label such an ethically complex revolution so naively is uncharacteristic of him, but his conclusions are more sophisticated and complex: that whatever may happen in the future, “each new truth the public learns is itself an irreversible step, a small but important widening of the borders of the permissible.” Whether or not Gorbachev survives, he intimates, perestroika will now lurch forward of its own volition.

The prime achievement of Smith’s book is that he explains so convincingly Gorbachev’s predicament in the heart of the Kremlin. In “The Hidden Nations,” political analysts Nadia Diuk and Adrian Karatnycky set out instead to study the U.S.S.R.’s troublesome extremities. They cover much of the same ground--Armenia, Azerbaijan, Uzbekistan, Lithuania--and the ethnic Russian backlash. But their treatment of the lesser nations is wider and fuller, with an important section on the vital republic of the Ukraine; and their survey of the economic inequalities among the republics produces a formidable barrage of statistical evidence to suggest that the Russians have exploited the minority nations.

Yet this book, while serious and detailed, lacks the authority, the thrust or the clarity of Smith’s. As is so often the case, two authors prove less focused than one; perhaps energy has been diluted by consensus. Whatever the reason, their study sometimes smacks more of conscientious collage than of digested experience; and some regions--notably Soviet Central Asia--interest them less than others.

Here, too, the near-instant obsolescence that threatens both books is most apparent. Already a host of upheavals has occurred since “The Hidden Nations” was finished: Armenia’s hardened stance on independence; the triumph of nationalists in the Georgian elections; the relaxation of the Soviet military pressure and embargo in Lithuania, and much else.

Nevertheless, this is a useful and usually balanced work that sounds a cautious note of optimism. As the subject nations of the U.S.S.R. begin to rediscover their identity, the authors write, the migration of ethnic Russians back into European Russia--searching either for jobs or for a greater sense of security--may increase the native hold on their own republics.

The book ends with a controversial trumpet blast against the near-silence of the West in the face of the republics’ moves toward freedom. As early as 1854, the Russian scientist Chaadayev was writing that “Russia moves only in the direction of her own enslavement and the enslavement of all the neighboring peoples.” For this reason, it would be in the interest of not only other peoples but also of her own that Russia be compelled to take a new path.

Few would deny the desirability of that. But the overt intrusion of the Western powers--replete with their own interests, ignorance and insensitivities--into this political labyrinth might produce results contrary to all intentions.

The future of the U.S.S.R. is impossible to predict, but our ignorance, at least, can be lessened. These two books add their shafts of light against the dark.