Washington — The ideological and political struggle for President Reagan's favor on defense spending has moved from the trenches onto the open battlefield in Washington.
In terms of manpower and rhetorical persuasion, it would appear that the forces of moderation are prevailing. But recent history and the longer view indicate that any change in plans for a continued military buildup will be a matter of degree and not fundamental.
On the right flank, Defense Secretary Caspar W. Weinberger is the lone Cabinet-level holdout for leaving the Pentagon untouched in the search for deficit reductions. Urging him on are the President's conservative soulmates - the Heritage Foundation and the Committee on the Present Danger. Both groups warn in recent reports that the United States is still in danger of falling behind the Soviet Union in military might.
Noting last week's Kremlin announcement that the Soviets will increase defense spending by 12 percent, Mr. Weinberger argues that to slacken the US buildup reduces the incentive for Moscow to be more accommodating. In recent interviews, the President has indicated that this is his basic position as well.
Tugging in the other direction are the same congressional and intellectual critics who have been faulting the size and shape of the President's ''rearm America'' program since Reagan took office.
Joining them in pushing for a smaller increase in defense spending for the coming fiscal year (nobody is talking about actual cuts) are Treasury Secretary Donald T. Regan, Budget Director David A. Stockman, and the entire House and Senate leadership. Republicans and Democrats alike (at least those with the most influence) are saying that cutbacks in projected spending to reduce the federal deficit must include defense.
''I don't believe you can put together a realistic package without including defense,'' Senate Budget Committee chairman Pete Domenici (R) of New Mexico told reporters at breakfast Tuesday.
There has been talk at the White House of reducing the Pentagon's fiscal 1986 request of $334 billion by as much as $10 billion. This would reduce the real (inflation-adjusted) rate of increase over the current fiscal year from about 10 percent to between 6 and 7 percent.
But Senator Domenici said that ''this is not going to do the job.'' He talks in terms of a $12 billion to $15 billion reduction, which would leave a real increase of between 5 and 6 percent.
The long-range administration
plan has been to hold annual Pentagon spending growth for the coming year to about the same level as the first Reagan term, when it averaged 9 percent. For the rest of Reagan's second term, when major down payments on many of the new weapons will have been made, defense spending is projected to drop to a 3- to 4 -percent annual growth rate.
Many experts warn against the typical pattern of military spending, in which major increases are followed by sharp cutbacks. This disrupts defense planning and can add to cost overruns.
''We're seeing it now,'' says former Defense Secretary Melvin Laird, who favors a defense increase of about 7 percent now and longer-range annual increases of 4 to 5 percent through this decade.
A former member of Congress, Mr. Laird says he believes the apparent improved atmosphere for US-Soviet arms control talks will influence lawmakers to restrain defense spending. On the other hand, he notes, the prospect for new negotiations may also win increased support for the controversial MX missile as a valuable bargaining chip. Key votes on the MX, which barely survived earlier votes on Capitol Hill, will occur this spring, just after superpower discussions are to resume. Another likely target for defense-budget cutters is likely to be the President's strategic defense initiative, or ''star wars'' program to defend against attacking nuclear weapons.
Congress this year approved $1.4 billion for research in this area, a cut of about $400 million from the Pentagon request. For the next fiscal year, the Defense Department is seeking an increase of nearly 100 percent in money for research in advanced missile defense technology to $3.8 billion.
Lawmakers in recent years have also resisted military payroll increases of the size sought by the Pentagon. They are likely to look closely at the proposed 7 percent pay raise planned for 1986.
From 1981 through 1984, Congress approved 97.5 percent of the Reagan defense spending program, according to the Congressional Research Service. This was some the same period.
It now may be harder to do, but the Defense Department is likely to continue accommodating congressional cuts by relying on lower inflation, trimming some programs, and stretching out others.