OF all the reverses in political pressures on Washington the biggest is on the defense budget. As recently as three months ago, Secretary of Defense Caspar Weinberger was still talking and behaving as though the sky was still the limit on defense spending, and he was still implying that anyone who proposed even mild trimming of the 1986 military budget must be a dupe of the KGB in Moscow.
Today there are unkind whispers heard even within the walls of the Pentagon itself. Both inside and outside the building there is a growing sense that Mr. Weinberger has hurt rather than helped the cause of a stronger military posture by having indulged in too much oversell.
The backlash has built up so suddenly and become so powerful that it has already imposed a freeze on the next Pentagon budget, to be the same as for the current year plus inflation but nothing over the inflation figure.
The reversal of attitude toward the defense budget was foreseen. Cap Weinberger was warned, repeatedly. Six former Republican secretaries of the Treasury and Commerce even took out newspaper ads back in 1983 warning of the dangers of ever-rising defense budgets both to the national economy and to President Ronald Reagan's policies.
At that time, Secretary Weinberger paid no heed. He kept on reaching for more. He kept on right up to this month of May. He was still demanding a 17 percent rise in net defense spending for 1986 when the great revolt in Congress blocked him into a freeze.
Now Mr. Weinberger has a new problem of his own making which will be more difficult than anything he has yet faced. He will have to allocate reduced funds among the jealous services. Worse, he will have to decide which guns are to be scrapped so that other guns can go forward -- because there will no longer be enough money to give each military service all it can spend.
For example, does it make sense to go on building B-1 bombers at $300 million each when the less vulnerable Stealth is in sight only a few years further along? And does a manned bomber make real sense at all when an unmanned air-launched cruise missile is cheaper and probably more effective?
There are more questions like that. Why build 100 MX missiles which are vulnerable when the Navy's new submarine-based missiles are not vulnerable and expected shortly to be just as accurate?
Mr. Weinberger has been spared the awesome problem of deciding between weapons and service functions by the luxury of being able to give each service what it wants. He approved MXs for the Air Force and 600 ships for the Navy and the M-1 tank for the Army, and lots of other high-cost new weapons.
But some of the new weapons have overlapping tasks. Mr. Weinberger's predecessors wrestled with the problems of priorities and relative need. Had Mr. Weinberger followed their example he would not have run the defense budget so high that it could be shot down.
The proper role of the secretary of defense is to get for each branch of the armed services the weapons it truly needs to perform its tasks. But it is also his function to see to it that needs are measured reasonably and that duplication of effort be avoided.
Mr. Weinberger has done little of the second job. Some would say, none. His critics accuse him of having acted not as a secretary of defense but as a salesman for the arms contractors. The B-1 bomber is known as an ``ideal weapon,'' not because of its prospective combat performance but because it puts contracts into 48 of the 50 states.
Such ``ideal'' weapons have had the priority in the Weinberger scheme of things. Once started they are almost impossible to stop. They eat up money which is needed for the unspectacular items. Ammunition stockpiles are still too low for safety. There are difficult times ahead at the Pentagon.