RICHARD PERLE is not a household name in grass-roots America, and he occupies a relatively modest job in Washington. But his departure from the administration this spring could prove to be an event of major importance - one that well should add to the misgivings of conservative Republicans about the last two years of the Reagan presidency. Mr. Perle's role as assistant secretary of defense for international affairs - a fourth-level post at the Pentagon - belies his true influence. For six years he was the driving force behind the most controversial aspects of the administration's security policies - the resistance to arms control, the reinterpretation of the US-Soviet Antiballistic Missile Treaty to permit extensive ``star wars'' testing in space, and an anti-Soviet economic strategy that precipitated the most serious crisis in the Atlantic alliance in a decade.
Conservative Republicans, fearful of a drift toward accommodation with Mikhail Gorbachev's Soviet Union, have good reason to anticipate Perle's departure with apprehension. With this youngish disciple of the late Sen. Henry (Scoop) Jackson gone, a spirit of moderation and compromise is likely to grow in Washington - particularly at a time when a President in trouble is eager for a foreign-policy success to help restore his image, pragmatists have taken charge in the White House and the CIA, and the Democrats have regained the Senate.
There is no one on the scene qualified to take over Perle's unique role as defender of the pure anti-Soviet faith - a role that has earned him the sobriquet of ``the Prince of Darkness.'' A neoconservative Democratic ideologue with a keen intellect, a persuasive tongue, an exceptional grasp of strategic issues, and outstanding skill at bureaucratic infighting, he has pursued a simple agenda with unrelenting doggedness. It is an agenda based on the premise that the United States and the Soviet Union are in a veritable state of permanent war and that America must behave accordingly.
Given that assumption, the very process of superpower arms control is deemed dangerous, because it tends to create a false sense of security and weaken the resolve of a democratic nation to sustain an adequate defense against an implacable Soviet military challenge.
Beyond that, Perle favors a US strategy aimed at undermining the Soviet economy, not simply by controlling the transfer of strategically valuable technology, but by curbing credits and any trade that might ease Russia's acute economic difficulties. He is, moreover, chronically impatient with US allies for their reluctance to embrace this doctrine.
While Perle has had only limited success in securing acceptance of a strategy of economic warfare against Moscow, he can claim striking success in shaping arms control policy. In the six years of the Reagan administration, no arms control agreements have been concluded. The unratified SALT II accord, denounced by President Reagan as ``flawed'' but still honored by his administration for five years, was repudiated last year. And, thanks to an ingenious maneuver initiated in large part by Perle, the administration is moving to gut the Antiballistic Missile Treaty.
The departing assistant secretary of defense helped engineer a move to reinterpret the ABM Treaty to permit testing of the President's Strategic Defense Initiative - which had before been universally regarded as barred by the superpower accord. Sam Nunn, chairman of the Senate Armed Services Committee, has warned that this maneuver could lead to a constitutional confrontation between the executive branch and Congress.
Perle has also employed his bureaucratic skills to forestall serious discussions in Geneva on what star-wars research is permissible under the ABM Treaty. US negotiators acknowledge that until this issue is resolved, talks over reductions in strategic nuclear arsenals will remain in a dead end.
Perle's resignation as full-time assistant secretary of defense - he will still be available as a consultant - will not automatically lead to a more pragmatic, less ideologically motivated approach to security issues. But a significant change is inevitable with the Prince of Darkness gone and with pragmatists such as chief of staff Howard Baker and national-security adviser Frank Carlucci running the White House.
At the very least, the voices encouraging a confrontation with Congress over the ABM Treaty, the star-wars program, and arms control policy can generally be expected to carry less weight. The President may even be persuaded that he cannot hope to realize his dream of major cuts in strategic nuclear arms without accepting constraints on the development of his other dream of a space-based defense system.
Joseph Fromm, a veteran foreign correspondent and editor at U.S. News & World Report, is a fellow at the Johns Hopkins School of Advanced International Studies.