The belated discovery or acknowledgment of 2,000 or 3,000 Russian soldiers in Cuba has at least momentarily rescued the opponents of SALT II from what looked like certain defeat.

Although the Soviet force has apparently been in Cuba for years, its sudden disclosure is a windfall for those who oppose the treaty, not on its intrinsic merits but on Russian behavior in general.

Nevertheless, Cuba aside, the crucial question is still whether the treaty is advantageous to the United States. Up until the new development, the SALT critics, having exhausted other arguments, were reduced to holding out for enlargement of the defense budget by 1 or 2 percent above the 3 percent increase already planned by the administration. As if that could make a serious difference in U.S. security.

Even if Congress as a whole were to appropriate the extra funds, which hitherto was doubtful, it is hard to see how that could materially alter the comparative U.S.-Soviet military posture, for the Pentagon has already indicated that any additional money would be spent more for refurbishing the military establishment than for beefing up strategic operations.

One of the more farcical developments is that some of the leading senators who are now demanding an arbitrary inflation of the military budget as their price for supporting ratification of SALT II were, only a few months ago, voting to cut the defense expenditures proposed by the administration.

The hawks in the House were also noticeably tame when its defense appropriations subcommittee, for decades a patsy for the Pentagon, slashed the military's request for additional funds by $2.2 billion. Chairman Joseph P. Addabbo (D-N.Y.) said he did not "share the point of view" that holds that SALT II "can only be ratified if it is accompanied by a massive increase in federal spending."

Much the same sentiment was expressed by the usually hard-lining Sen. Robert Dole (R-Kan.). In writing President Carter a surprisingly unpartisan letter about SALT, Dole said he meant to suggest that he was "not certain" that the proposed increases in military spending were either needed or can be wisely spent.

The puzzling fact is that the Pentagon doesn't seem to know what to do with the unspent billions already in its pipeline. Addabbo reports that the Defense Department has accumulated $22 billion in "unobligated" balances for weapons on which no contract has been awarded.

Moreover, he notes it has piled up $88 billion in "unexpended" balances for projects on which contracts exist, but money has not been disbursed. All these funds can be shifted around to avoid the scrutiny of Congress.

Many old Pentagon hands agree that what is really needed is not bigger but better spending. Addabbo says, "You could probably have 3 percent growth without increasing the dollars. There's enough fat." There is, indeed.

Congress is openly perturbed over the Pentagon sending an ever-expanding legion of dependents to Europe, which now includes 378,000 wives and children of service personnel. The cost to the Army alone is put at $824 million. A new Budget Office report warns against abuse of the military retirement system, which has allowed 40 to 50 percent of retiring generals and admirals to leave on costly disability.

A Brookings study found the Pentagon could save over $900 million a year by eliminating overpayment of its blue-collar workers. A presidential commission found that $10 billion a year could be saved by overhauling the military pension system.

Between now and 1984, Carter's defense budget is expected to rise to $197 billion a year, an increase of $67 billion. Inflation could make it much larger. If the Senate cold warriors succeed in forcing a still bigger increase, will America's strategic strength be decisively greater?

Gen. David C. Jones, chairman of the Joint Chiefs of Staff, doesn't think such extra money is needed for "glamorous" new weapons programs. He would favor spending it on "a lot of mundane things" such as spare parts, ammunition and training for conventional purposes.

If the American public is confused by all the conflicting statements, it has good cause to be. Military statistics can be deployed to prove almost any case.

In testifying before Congress on Feb. 21, Defense Secretary Harold Brown said: "Defense has not grown and is not growing at the expense of other federal programs . . . . Since 1967 . . . defense has shrunk to about its pre-Vietnam levels. Measured in constant 1972 dollars, defense obligational authority is today 1.1 percent below that of 1964."

But then on March 8, the associate director of the White House Office of Management and Budget said, "I am happy to report to you that, under President Carter, defense resources and forced have risen steadily. We have increased the real level of resources actually devoted to defense to recover from a number of years of decreasing defense budgets . . . . Under President Carter's leadership, we have set a course of steady real growth."