WHEN THE DEFINITIVE history of Soviet-American efforts to negotiate an end to nuclear testing comes to be written, it will be 1) very long and 2) replete with incidents of brass-knuckle bureaucratic warfare. The current episode involves a campaign to get Jimmy Carter to weaken the comprehensive test ban that he is negotiating with the Russians (and British) at Geneva. The campaign is led by the two nuclear-weapons labs - Los Alamos and Livermore - and their sympathizers in the departments of Defense and Energy. They are moving, it seems, on two fronts.

First, the labs contend that a treaty should let the United States conduct occasional underground tests to check the quality of stockpiled warheads. But, a group of former top Los Alamos hands has told the president, the necessary stockpile assurances can be gained by measures other than nuclear testing - by non-nuclear testing, inspection and remanufacture of suspect units. Our own view is that whatever marginal confidence, if any, might come from testing does not seem worth the costs in strategic and political instability. President Carter, we understand, feels that way, too.

The labs further argue that, if a comprehensive test ban is completed, it should run for only three years, with the presumption that test should then be renewed. Mr. Carter is apparently under pressure to throw the testing lobby that bone. We hope resists. A short ban would undercut his no-test pledge. A short ban accompanied by an expection of resumed testing would nock everything he has ever said about the nuclear menace. With China, for one, still not recruited to the Geneva talks, it makes some sense not to write an indefiniate ban. But a ban must be of respectable length. Five years is minimal.

A comprehensive test ban seems to once so familiar, for having been discussed for two decades, and so modest, when set against the strategic arms limiation talks, that people's attention wanders. It may help to underline a few basic things. To continue testing warheads underground is at this point merely to drive the arms race mindlessly on. A test ban would freeze what almost everyone regards as the current American advantage in warheaded technology. A ban would strengthen the two power's hand in inducing other countries not to start or expand nuclear arsenals. The treaty under negotiation embodies longsought Soviet decisions to permit on-site inspections and to forego "peaceful" explosions.

For political reasons, a test ban may have to stand in line behind a SALT treaty, but, meanwhile, anxious would-be testers are trying to beat down the American negotiating position. It must not happen.