DESPITE A rousing address by Defense Secretary Caspar Weinberger, there were rumblings of discontent about the mounting size of the defense budget among top corporate executives meeting this past weekend in Hot Springs, Va. Executives told a reporter that they, like almost everyone else, know little about the specifics of the defense budget. But they know that if you want a buildup of the magnitude sought by the administration, and you also want to avoid crippling inflationary pressures, you must raise taxes to pay for it. And that would mean raising taxes so high as to impede economic growth.

This is a widely felt concern, but it is one that only the administration can really respond to. Congress, for both institutional and political reasons, simply cannot do major overhauls on the defense budget. Congress can, and did this year, trim here and there. But saving substantial money without impairing defense readiness requires a close weighing of threats and allied capabilities and then an efficient structuring of U.S. forces. Only the president and the Pentagon can do that.

This year, for example, Congress is trying to reduce 1983 defense spending almost $9 billion below the administration's request. The bill reported by the Senate Appropriations Committee shortly before Congress recessed claims to meet that goal. But there is less in those savings than meets the eye. The only new weapon that didn't get the go-ahead was a new kind of lethal nerve gas bomb. The rest of the savings come mostly from faster phasing out of obsolete weapons, delaying additional funds that probably wouldn't have been spent next year anyway and a measure of budget flimflam.

For example, more than $1 billion in savings comes from deferring a decision about how to cover authorized military pay increases. That's likely to get added back on to the budget next year. Another billion or so comes from a sudden recognition by the Pentagon that fuel costs have leveled off. That kind of last-minute discovery nourishes the suspicion that the administration's defense budget is reasoned from a preestablished spending goal rather than from a careful assessment of actual needs.

Meanwhile, President Reagan is out on the stump making the one argument that should never be made in defense of a defense budget. Don't vote for the Democrats, he told workers in depressed Ohio, because they'll cut the defense budget, and that will cost you jobs. Not only does defense, dollar for dollar, create fewer jobs than almost any other kind of spending, but to treat defense spending as pork cheapens the legitimate claims of national security. If the administration wants to maintain a consensus behind improving defense preparedness, it will have to make a better case