TWO SEPARATE SORTS of explanation came out of the Pentagon as a result of the two recent false alarms within one week in the computer system that warns the United States of an impending nuclear attack. Defense Secretary Harold Brown hastened to assert that the United States is not going to be tricked into going to nuclear war by a computer on the blink.Other systems were available and were used to discover that the alarm raised by one computer was false, and anyway the key decisions in the sequence leading to an American decision to fire a nuclear missile are made by human beings. Meanwhile, Gen. David C. Jones, chairman of the Joint Chiefs of Staff, added that the false alarms, and the predetermined readiness steps the United States took as a result of them, should convey to the Soviet Union that the United States can respond quickly to a real threat.

As between trying to make these unfortunate events, first, assure people everywhere that the United States has the control to prevent an accidental, unauthorized nuclear shot and, second, warn Moscow that the United States has the control to fire a timely authorized shot, the Pentagon has dealt passably well with the particular anxieties at hand. But, even leaving aside the propaganda the Soviet Union is now trying to make of the two incidents, its explanations are finally inadequate. That humans and not computers decide to fire back does not obviate all possibility of either computer error or human error. That the command and control system gives the president a firm grip on the nuclear trigger does not ensure either effective deterrence or effective defense. One can only speak in terms of probabilities. Reliability is a matter of degree.

Sen. Tower, professing concern, wants the Armed Services Committee to look into the false alarms. Good. No prudent person can fail to be concerned about the workings of the nuclear-alert system. The false alarms do not necessarily indicate that something serious is wrong. It is reassuring, after all, that in two successive incidents, and in a third last November, and in however many the Soviet, Chinese, British and French nuclear-alert systems may also have experienced, the alarms have been found to be false before any irreversible responses were made. Nonetheless, the alarms are "useful." They stand as a general warning of the need for the utmost care in the treatment and handling of weapons of mass destruction. They should remind those resonsible for them of the risks of taking for granted the instruments and procedures that have been devised for their control. As long as nuclear war is possible, it makes sense to be on nuclear alert.