For all his commitment to military buildup, President Reagan has shown that he can be wary of grandiose, misguided weapons schemes. For example, he turned away from the previous administration's elaborate MX basing mode although clinging to development of the controversial missile itself. He ought to redouble efforts at exercising the utmost discrimination among various weapons programs in light of a lengthening list of cautionary voices, to which Murray Weidenbaum's was added last week.
Mr. Weidenbaum spoke to the Associated Press in an interview he asked to be withheld until after his recent official departure as chairman of the Council of Economic Advisers. The federal budget really has not been cut, he said. Slashes in social and other nonmilitary spending have been offset by the unprecedented growth in military spending sought by Mr. Reagan. Thus economist Weidenbaum lent fuel to those who argue that the administration's budgetary approach is more in pursuit of ideological than economic ends. And he added that when the military spending is combined with the big tax cuts the result is ''horrendous'' deficits.
Then the interview came to another point being made by many: that military crash programs ''rarely increase national security.'' Instead, they ''strain resources, create bottlenecks.''
In those few words Mr. Weidenbaum hinted at quantities of economic analysis and nudged attention toward bipartisan ways to achieve more rational military spending alternatives.
The analysis involves such problems as the skewed and inflationary competition for personnel and materials when huge military programs descend on the private marketplace.
The alternatives involve, for one thing, choices between weapons systems that are big and complicated or lean and simple. The United States doubtless needs some of each.
For aid in cost-conscious choosing, Mr. Reagan can look not only to a former aide like Mr. Weidenbaum and a present aide like budget director David Stockman (remember how in that notorious Atlantic Monthly interview he was pictured as hitting the ceiling when he lost his argument for braking Pentagon spending?). The President also can consider the views, for example, of Congress's virtually unsung ''military reform caucus'' headed by Representative Whitehurst (R) of Virginia and founded by him and Senator Hart (D) of Colorado.
The caucus is trying to encourage the fundamental debate over military concepts. It stresses maneuverability, substituting ''speed for tonnage and ideas for blood.'' It seems to be somewhere in the same ballpark with the panel of high-ranking officers from the Army and Air National Guard who came out for simpler, more reliable weapons not so long ago.
Is Mr. Reagan listening? Tomorrow's state of deficits and defenses will tell the tale.