Politically, the meaning of President Reagan's speech the other evening is that he intends to buck the tide of popular and congressional questioning of his defense budget. He is not going to do the easy popular thing and bend, or, if he is, he is going to do it only later and with the greatest reluctance. Meanwhile, he is going to force his critics to justify every nickel they want to cut. His speech showed him in his most stern, forceful and overtly political mode, and it is hard to think that, among many who watched him, he did not bolster his case.

It was not, however, a speech likely to still all serious doubts about Mr. Reagan's course. He presents his budget as one that cannot be trimmed except by "cutting our commitments to allies or inviting greater risk or both." In framing the choice in this way, the president has a certain point. Most Americans do not seem ready to cut commitments to allies, although there is necessarily a continuing discussion on the manner of supporting them. People who are aware that the world is risky enough already, cannot wish to "invite greater risk." If the Reagan framework is accepted, he wins hands down.

But his terms are far from universally accepted. He simply has not made the case that American foreign policy and the citizenry's relative peace of mind dictate his level of defense spending. Part of his trouble is his way with numbers and comparisons. For example, he says that since the United States introduced its last new intercontinental missile in 1969, the Soviet Union has built five new classes of ICBMs and upgraded these eight times; he ignores the whole American multiple-warhead program, and much else.

By using "bad" numbers he devalues his "good" ones. The overall effect is one of stretching the facts and losing credibility. It says worlds that a natural potential ally like Sen. Sam Nunn (D-Ga.) faults him "for not taking into account America's strengths, the strengths of our allies and the weaknesses of the Soviet Union."

Then there is the administration's continuing inability to establish public confidence in its procurement procedures. Do you know anyone who feels the United States gets anything near a dollar's worth of defense for each dollar spent? Mr. Reagan in his address slipped past this problem. Yet many in Congress are transfixed by it, as you could expect them to be during a period of high political strain over budget-making. It remains for the president to find more effective ways to address the source of their concern.

From listening to President Reagan, you would scarcely know that congressional support for substantial defense spending, and for substantial increases, remains steady. This is not a little surprising, given the economic and political landscape. Rather than arguing for a surge that the defense establishment appears unprepared to put to good use, at the moment, Mr. Reagan should cultivate conditions suitable for maintaining a strong defense over the long haul.