Washington — During the first three budget exercises since Ronald Reagan was elected President, congressional critics cried, ''Cut the Pentagon budget!'' Then they pretty much gave in.
Republicans on Capitol Hill, in concert with the since-dispersed ''boll weevil'' Democrats, stood behind their man in the White House during debate on the '81 supplemental budget, as well as the '82 and '83 budgets.
That is not happening this year, however, nor is it likely to happen. Most Senate Budget Committee Republicans are joining Democrats in saying the rate of increase in defense spending should be about half what the administration wants. A conservative Republican has taken the lead in demanding an investigation of persistent reports (including internal Pentagon studies) that the Reagan military buildup will cost a lot more than projected. Even the normally hawkish House Armed Services Committee has voted a slower rate of growth in defense spending than the President wants.
Ironically, the Pentagon's recent report on Soviet military power may push the tussle over the military budget further in this direction. A more balanced study than its 1981 predecessor, it includes data comparing NATO and the Warsaw Pact, thereby presenting a less ominous overview. Also, it acknowledges that Moscow is having serious economic difficulties that affect its military buildup - that the industrial growth of the Soviet Union has fallen ''to a post-1945 low.'' And it notes that Soviet forces are encountering tough problems in Afghanistan and taking heavy losses.
While urging lawmakers not to cut his budget, Defense Secretary Caspar W. Weinberger says he is happy to report that the United States ''has begun to close the gap,'' making up ground it may have lost to the Soviet Union in recent years.
But it will take ''a good five years'' to attain a credible and effective strategic and conventional deterrent, he said. And Mr. Weinberger acknowledged that ''it's very hard for the American people to want to stay on paths like this for more than a year or so.''
Does this mean there will be major cuts in defense? Don't look for anything startling (like the cancellation of new aircraft carriers or the B-1 bomber).
''Congress has never - in either house - voted 'cold turkey' to cut a major weapon,'' says Rep. Les Aspin (D) of Wisconsin, a member of both the Budget and the Armed Services Committees in the House.
More likely, the rate of growth in military spending will be held to a lower level, something closer to 5 percent (minus inflation). The White House is seeking a rate in excess of 10 percent.
Much of this has to do with an increasing sense that the cost of the proposed US rearmament is likely to be higher than the administration says. Last year, the Defense Department used lie detectors to find out who was saying such things in the Pentagon. Yet a senior defense official meeting privately with a few reporters recently acknowledged that costs may indeed go higher than forecast. Several days later, another official confided that the Office of Management and Budget ''differed substantially'' with the Pentagon over how much would be saved by buying certain major weapons under multiyear contracts. The OMB says defense officials may be overly optimistic.
In a series of recent hearings, a civilian Pentagon analyst has been telling fascinated lawmakers that the historical problem of underfunding and cost overruns is likely to continue unless significant changes are made in the way the country buys its weapons.
This has led Sen. Charles Grassley (R) of Iowa to press for investigations by the General Accounting Office and the Congressional Budget Office.
Two other significant signs:
* Republican-led Senate committees that oversee federal spending have recommended spending $9 billion more for domestic programs than has President Reagan. While initially agreeing with the Pentagon's spending request, the Armed Services Committee (chaired by defense hard-liner John Tower of Texas) reported that ''this recommendation should not be considered a blanket endorsement of all the programs and policies contained in the President's budget.''
* With cost considerations in mind, the Defense Department itself has slowed the pace of some weapons buying. ''This year's budget has substantial reductions in shipbuilding,'' says Barry Blechman of the Roosevelt Center for American Policy Studies, noting that the Navy's five-year plan includes 21 fewer ships than in '82. ''The number of aircraft they're buying is also less.''
Congress last year nibbled away the Pentagon's request for a 13 percent spending increase, pushing it back to a still substantial 9 percent. By the end of the budget cycle, lawmakers had raised the cut from $8 billion in their initial budget resolution to $17 billion. This trend is likely to continue with greater force this year.