IT has taken only one month from election day to disclose that there are two things President Reagan wants which he cannot have, even though he won the biggest Electoral College vote in the history of the United States.
He wants to reduce the federal deficit without raising taxes and without cutting his defense budget. Congress will not have it. His own Republican leaders in Congress agree with the Democrats that it would be politically impossible to ask for more cuts from those who receive welfare - or from programs benefiting the financially strapped middle-class - without also taking more from taxpayers and the Pentagon.
We are a long way from being able to see how all this will sort itself out during the coming session of the Congress. Few political battles in Washington are fought with the determination and fierceness of those over taxes and guns. To have two such battles in one Congress will provide the drama of the coming session - and plenty of it.
It is too much to hope that in approaching the prickly problem of where to cut the military budget Congress will approach its task exclusively from the point of view of what is needed to support a rational national military strategy. That is what would happen in an ideal situation. It seldom happens in a political democracy, where each congressman and each senator is acutely aware of the contracts that can flow or not flow into his (or her) individual district.
Far too often the key question is not whether a given contractor can produce the best weapon, but where that contractor will place the contracts and subcontracts. By judicious distribution of contracts and subcontracts a majority of votes can be mobilized for almost any weapon, no matter how redundant.
During the recent campaign it was noteworthy that Sen. Alan Cranston (D) of California defended the B-1 bomber, which is assembled in southern California, and had the support of Sen. Howard Metzenbaum (D), whose state of Ohio produces the engines for that same questionably necessary and very expensive weapon. Senators Cranston and Metzenbaum tend to be listed as ''doves'' on their general voting record, but certainly not when juicy contracts for California and Ohio are involved.
It was ever thus. It will continue to be so in the future, and certainly during the session of Congress just ahead. It is part of the price we pay for democracy that we sometimes choose our military weapons for the wrong reasons.
It is doubtful, for example, that we need both the B-1 and the ''stealth'' bomber, which is scheduled to come after it. It is more questionable whether any manned bomber is needed at all in these days of increasingly accurate ballistic and cruise missiles. Why plan to send men deep into heavily defended hostile territory when unmanned weapons can be just as accurate - and cheaper?
Then there is the question whether any land-based ''deterrent'' will be justifiable when the Navy's Trident II missiles come on line with an expected accuracy equal to that of the big land-based ICBMs. The strongest argument so far for MX is that the land-based deterrent is more accurate than the sea-based.
But Trident II is expected to equal the MX in accuracy. And the Trident submarine is the least vulnerable vehicle for the deterrent. A fixed land-based ballistic missile, particularly one fitted with multiple warheads, acts like a magnet for hostile attack.
If the generals and admirals had their way, more money would be spent on conventional weapons and less on the expensive nuclear weapons. But there are fewer political plums.
The greater danger in the arms debate ahead is not that there will be too few to impress the Russians. It is that too much taxpayer money will still be wasted.