Washington — As its nuclear weapons and arms control strategy evolves, the Reagan administration finds that it has two adversaries.
One is the Soviet Union, against which US warheads are aimed. The other is a significant portion of the American public, which has become increasingly anxious over the prospect of nuclear war, frightened over the buildup of the US arsenal, and frustrated by the lack of serious negotiation between the two superpowers.
This is clearly obvious in the US Senate, where any arms control treaty will have to be ratified and where hearings on the mounting number of congressional proposals have just begun.
''A society that has traditionally regarded war as too important to be left to generals now seems to be saying that arms control is too important to be left to governments,'' Senate Foreign Relations Committee chairman Charles H. Percy (R) of Illinois said as hearings began.
The committee this month will consider what Mr. Percy calls ''the extraordinary number of arms-reduction resolutions that have been introduced in recent weeks.'' It is also expected that the administration soon will present what Defense Secretary Caspar W. Weinberger calls ''far-reaching proposals for intercontinental arms.''
The White House May 3 said President Reagan will accept Soviet President Leonid Brezhnev's invitation to hold a summit conference in October.
The domestic public opinion and political problems faced by the administration are becoming clearer. Congress has voted to cut proposed funding for the MX missile and increases in civil defense spending. There is mounting criticism from Republicans as well as Democrats over the lack of what Ronald Reagan as a presidential candidate said would be ''immediate'' arms-control proposals. A recent Washington Post-ABC News poll shows Americans by a margin of nearly 3 to 1 favor an immediate nuclear freeze by both the US and the USSR.
But the same survey indicates why the administration itself must find the issue frustrating. Most of those polled also believe the Soviet Union is ahead of the United States in nuclear weaponry and are sure the USSR would violate a nuclear freeze.
In his most recent statements, Secretary Weinberger is taking a somewhat softer posture than was found in earlier administration rhetoric. ''We entertain no illusion about nuclear conflict,'' he told senators. ''Everyone would lose in such an event.''
Addressing the delay over presenting a detailed arms-control proposal, he said: ''Actually, we have gained time . . . by initiating a coherent, long-term program to improve the stability and security of our deterrent nuclear force, thus providing the only basis for negotiations that can lead to real reductions, and the incentive for the Soviet leaders to take our proposals seriously.''
Here too, however, there is great difference of opinion.
''We have lost valuable time and we have lost the political initiative,'' says James Schlesinger, secretary of defense in the Nixon administration. ''I believe that it is not only a moral but a political necessity that the United States . . . be seen as continuously ready to negotiate arms control agreements.''
It also seems that every senator, former diplomat, and retired senior military official has developed a plan for reducing the threat of nuclear war.
Most recently, Adm. Noel Gayler (USN, ret.) has proposed deep weapon-for-weapon cuts in the Soviet and US nuclear arsenals. Writing in the New York Times Magazine, the former director of the National Security Agency warned that ''time is running out . . . we need a fresh approach.''
There are plenty of fresh approaches being offered, including (1) freezing the arms race now and negotiating, (2) negotiating first, then freezing, (3) prohibiting the production of weapons-grade plutonium, and (4) establishing a new US-USSR communications center to avoid accidental nuclear war.
But some old suggestions are being dusted off as well, including the SALT II agreement. This treaty was signed by US and Soviet leaders, but the US Senate refused to ratify it. Both countries have tacitly agreed to its terms, and a growing number of senators (including some who originally opposed it) see formal ratification as a good first step to future arms reductions. They note that under SALT II the Soviet Union would have to dismantle 250 of its existing strategic nuclear launchers.
The administration response is that America must ''arm to disarm'' by first increasing the US nuclear arsenal.
Like many other defense experts, Dr. Schlesinger says there still is ''rough equivalence'' in US and Soviet strategic weapons. The USSR has more intercontinental missiles and better ''hard target kill'' capability, but the US has more deliverable warheads, a superior and less-vulnerable submarine force, and a better mix of land-based, airborne, and undersea strategic weapons.
The key point regarding the issue of superiority, says Schlesinger, is that the US ''has and will continue to have . . . the ultimate deterrent.'' These are ''sufficient surviving and deliverable weapons to destroy the urban-industrial base of the Soviet Union--even after absorbing a Soviet strike.''
The full Senate is expected to consider a resolution on nuclear arms reductions before the end of May.