Washington — In Washington, the ``Weinberger Letter Affair'' has become a first-class political commotion. Last Saturday a letter from Defense Secretary Caspar W. Weinberger to President Reagan, urging firmness at the Geneva summit, found its way into the press. Now the Pentagon has mobilized to search for the leaker, and defense officials all over town are doing their best to look innocent.
If the leak came from the Department of Defense, ``we will fire the guy,'' grumbled spokesman Robert Sims on Monday.
But the letter itself was remarkable only for the timing of its release, not for its substance, judge experts here. It simply summed up the guiding principles of the hawk faction of the Reagan administration, which is widely considered to be led by Mr. Weinberger and Richard N. Perle, assistant defense secretary for international security policy.
``Its points have been Cap's position'' all along, said Gerard Smith, chief US negotiator of the SALT I treaty, at a breakfast for reporters.
The letter's main theme was that Soviet cheating on arms treaties requires ``appropriate and proportionate responses'' by the US. Weinberger urged the President to not promise continued adherence to the SALT 2 Treaty and to not be bound by restrictive interpretations of the 1972 Antiballistic Missile Treaty.
The letter also said congressional cuts in Strategic Defense Initiative (SDI) funds could put the US in a ``vulnerable and dangerous position'' when Soviet violations are taken into account. It suggested Reagan might submit a special supplemental defense budget this year.
The theme of Soviet treaty noncompliance has been sounded by hard-liners almost from the first days of the Reagan administration. It is a theme that looks at only the dark side of the issue, complains Mr. Smith. ``You always hear about Soviet cheating. You never hear about Soviet performance under these agreements,'' he said.
According to a recent report by the Arms Control Association, a private organization, the USSR may have committed such SALT violations as deployment of a non-allowed type of missile and coding of radio signals sent by missiles during tests. But the Soviets have strictly complied with the most important part of the treaty -- its limits on weapon numbers -- says the report. To stay within SALT boundaries, more than 1,000 Soviet long-range missiles and 13 missile-firing submarines have been dismantled sinc e the early 1970s, says the Arms Control Association.
The US might do itself a disservice to scrap SALT II, since the Soviets are testing four new types of missiles to the US's one, says the report. Absent treaty limits the USSR might be able to add some 7,000 warheads to its stockpile in the next 10 years. The US would only manage a 2,200 warhead increase, according to the report.
In his letter, however, Weinberger says that in the short term, adherence to SALT II would require the US to dismantle larger numbers of modern weapons than the Soviets, as new Trident subs and MX missiles are brought on line.
Administration officials who favor a tough line against the Soviets have also long complained that the USSR breaks the ABM Treaty with impunity. They point particularly to a large new radar in Siberia and say the Soviets may be poised to break out of the treaty and erect a crude nationwide ballistic-missile defense.
This is the third time in the nuclear age US planners have worried about Soviet defensive abilities, points out Michael Krepon, an expert on verification and compliance at the Carnegie Endowment for International Peace. In the early 1960s, such concerns led to the ABM Treaty itself. The second time, shortly after the treaty was signed, also involved unexplained radar activity and was eventually resolved in private discussion.
There is reason to be concerned about Soviet moves toward strategic defense, says Mr. Krepon -- their computers, sensors, and ground-to-air rockets are all more sophisticated today than they were in the 1960s and '70s.
But such concerns are arguments for shoring up the ABM Treaty, not threatening it, Krepon says. ``If you are concerned about Soviet territorial defense -- the ABM Treaty is the first line of defense against that,'' he says.
In his letter, Weinberger said he was concerned that a restrictive interpretation of the ABM Treaty would ``diminish significantly'' the US's own strategic defense effort.
In testimony to Congress on Oct. 30, SDI chief Lt. Gen. James Abrahamson said a US missile shield could not be fully developed without changes in the treaty.
By the 1990s, SDI is scheduled to test such large technology components as rockets launched from space platforms. Such tests, said General Abrahamson, would contravene the ABM Treaty, as traditionally interpreted.