MORTAL RIVALS Superpower Relations From Nixon to Reagan By William G. Hyland Random House. 272 pp. $19.95

IN THE HEADY days of Henry Kissinger's secret diplomacy, recalls William Hyland, President Nixon suggested that perhaps the members of the National Security Council staff should wear uniforms. Nixon proposed a blue blazer with an NSC emblem.

The plan for an NSC uniform was dropped, but the Nixon-Kissinger concept of the NSC staff as the president's action-arm -- able to get things done while the bureaucracies at State, Defense and the CIA spun their wheels -- has survived to inspire and bedevil the current administration. Hyland reminds us that for all its dangers, this NSC cult of secrecy allowed Kissinger to achieve his greatest triumphs: "De'tente . . . worked because it was implemented not by a cumbersome bureaucracy but by a small group, operating mostly in secret, with a relatively free hand, and backed by the immense authority of the presidency."

While nominally a study of Soviet-American relations, Mortal Rivals is largely devoted to an analysis of Kissinger's statecraft. Hyland writes not as a dispassionate observer, but as a member of the Kissinger team, at the NSC and then at the State Department. He advises the reader up front that "without {Kissinger's} friendship, this book would not exist at all."

The book covers what will be, for consumers of the memoirs of former government officials, rather familiar ground. Kissinger himself has not been shy about discussing his diplomatic accomplishments, producing two long and engaging volumes of memoirs, running to 2,804 pages. Thanks to Henry, we've already sat in the treehouse with Leonid Brezhnev, shooting wild boars at nearly point-blank range, watched Leonid's unsuccessful attempts to stop smoking, listened to Leonid tell anti-Semitic jokes. And we have heard Henry explain his lofty goal of establishing a "structure of peace" with the Russians.

Hyland's book is engaging, in part, because it offers a boiler-room view of the Kissinger years. It is a tale of high diplomacy, written by one of the low-profile aides who stayed in the background taking notes, writing position papers, and carrying briefing books. In Hyland's world, a 1973 presidential trip to Moscow is memorable as much for the broken toilet in Hyland's room as for the momentous events of the day; a 1974 trip to Vladivostok leads him to reflect on the staff man's difficulty in getting anything to eat late at night after the great men have finished their work. If Hyland, the staff man, harbored any resentment toward his boss, Kissinger, it doesn't show in this book.

What distinguishes Hyland's book is his effort to analyze what the de'tente era was all about. He does this, in some ways, more successfully and convincingly (and certainly with greater brevity) than has Kissinger himself.

The central theme of Kissinger's strategy, in Hyland's account, was the opening to Communist China and the resulting opportunity for "triangular diplomacy," with the United States playing off the Chinese against the Russians. Hyland suggests that Moscow's preoccupation with China was a continuing theme during the Nixon administration, starting with Soviet ambassador Anatoly Dobrynin's remark to Kissinger in early 1969 that China posed the biggest security problem for the Soviets, and ending with Brezhnev's private plea to Nixon in June 1974 for an anti-Chinese alliance between Moscow and Washington.

Kissinger's breakthrough was to understand that the United States could exploit this Sino-Soviet rivalry by opening relations with China. "The core of the new policy," writes Hyland, "was a classical reversal of alliances, in which China, in effect, joined the West against Russia."

The other great theme that runs through Mortal Rivals is the Soviet drive for nuclear parity and America's sometimes awkward attempts to live with it. Hyland describes the intricate (and in many ways counterproductive) early SALT negotiations with the Soviets, and the mounting political opposition at home to Kissinger's policy of de'tente.

Even now, Hyland seems peeved at the Congressional opponents of de'tente. His book contains as unflattering portrait of the late senator Henry M. "Scoop" Jackson, who ran for president in 1976 partly on his campaign to withhold trade benefits from the Soviets until they allowed more Jews to emigrate. Hyland argues that Soviet Jews paid for Jackson's political grandstanding. "In the end, Jackson was dead wrong, and tragically so," contends Hyland. "Jewish emigration was a shrewd cause to exploit, but the exploitation was too cynical."

HYLAND's enthusiasm for Kissinger leads to a truncated, and for this reader, inadequate, discussion of the dark days of Vietnam. Hyland notes: "By the spring of 1969, the Nixon administration had decided to seek a settlement in Vietnam rather than fight to the bitter end." A face-saving withdrawal was Kissinger's goal from the beginning, in other words. Hyland does not record that more than 15,000 Americans were killed from 1969 until the Paris peace accords were signed in January 1973 -- to achieve a settlement not very different from what the United States could have obtained at the beginning.

Hyland's discussion of the conduct of Soviet-American relations in the post-Kissinger presidencies -- Carter and Reagan -- is brief and serves mainly to demonstrate how far we have fallen from the Kissingerian heights of manipulative diplomacy. Indeed, the book offers little enthusiasm for the future of Soviet-American relations (the most Hyland can say in his penultimate paragraph is that "the United States has no reason to be ashamed of its efforts"). And it's interesting to note that these days, Kissinger himself is spending considerable time attacking some of his own creations such as the ABM treaty.

Still, Hyland is right to credit Kissinger for establishing a diplomatic framework "which not only survived {him} but is still the fundamental feature of international politics." The superpower agenda of arms-control, regional issues and human rights dates from the Kissinger era. Many of the leading foreign-policy practitioners -- in both parties -- are former Kissinger aides. And for Hyland, who watched Ronald Reagan trash Kissinger in 1976 and 1980, it must be satisfying to note that today, in the Reagan presidency, "conduct of Soviet policy still rests on the Kissinger foundation." ::

David Ignatius, an associate editor of The Washington Post, is the author of a forthcoming spy novel, "Agents of Innocence."