Minutemen III missiles carry three independently targeted warheads, not six, as reported incorrectly Wednesday.

President Reagan's dramatic new proposals yesterday for big reductions in Soviet and American nuclear missiles could, if accepted by Moscow, go a long way to reducing the fear of nuclear war.

If the president succeeds in getting the Soviets to reduce their stockpile of big land-based missiles that threaten this country's News Analysis News Analysis force of smaller missiles, then Americans can breathe easier. The temptation of either side to strike first would be greatly reduced and maybe eliminated because neither side--after reductions--would have an obvious advantage.

So in one sense, the plan is a would-be step to nuclear de-escalation.

But it will almost certainly not be an end to what most people would call "the arms race." The new proposals probably will still mean footing the bill for expensive new MX, Trident II and cruise missiles as well as new B1 and Stealth bombers.

For example, administration officials say the United States will propose that each side gradually reduce to about 850 the total of missiles based in underground silos and on missile-firing submarines. Such a reduction would be gradual, taking perhaps five or 10 years. The United States now has roughly 1,700 such missiles and the Soviets 2,400.

But the officials also say privately that those future 850 U.S. missiles could well be 200 big new MX missiles and 650 of the new Trident II missiles. These could replace the existing 1,000 Minuteman land-based ICBMs and hundreds of the current Poseidon undersea missiles.

Similarly, while the United States is prepared to discuss bombers and cruise missiles in the new talks with Moscow, these weapons will come under ceilings rather than be eliminated. Thus, the new B1 and Stealth bombers are still viewed as necessary replacements for the old and existing B52s.

In other words, although no details were discussed about what the United States might give up in the negotiations, the administration believes that if America is to have smaller forces, they must be thoroughly modernized so that they continue to deter attack and are able to retaliate with confidence if necessary.

Reagan alluded to this in his speech when he talked of "the monumental task of reducing and reshaping our strategic forces to enhance stability . . . ."

In briefing reporters yesterday on the president's proposals, officials said the idea was to keep them clear and understandable so they can "command public support." That will not be easy because the subject is extremely complex and because Soviet and American missile forces have big differences.

In general terms, what the president is proposing is a plan that stresses eventual equality in striking power and seeks, above all, to reduce or remove the big Soviet lead over the United States in very large land-based missiles.

Of the roughly 2,400 Soviet missiles, 1,400 are land-based. This includes 308 of the huge SS18s, each of which carries 10 atomic warheads. The United States has nothing to match this weapon. There are also 450 four-warhead SS17 and six-warhead SS19 missiles.

The 1,700 U.S. missiles include the land-based Minutemen and 52 older Titan missiles already scheduled for retirement. The rest are on submarines. Many U.S. specialists say the American missile force is less of a threat to Moscow's missiles than the Soviet force poses to this country.

Officials say that each side now has roughly 7,500 individual warheads on land and sea missile forces. Until now, a figure of roughly 9,000 warheads for the United States and between 7,000 and 8,000 for Moscow has been used in official statements. The difference, officials say, is that the 7,500 figure does not include bombs carried on long-range bombers of both sides. The initial thrust of the U.S. proposal is to focus on the most destabilizing weapons, meaning Soviet land-based missiles, which are most accurate and therefore the gravest threat to knock out the Minuteman in a first strike.

The president proposes reductions to an equal ceiling "at least a third below current levels" of warheads. In effect, this means a cutback from 7,500 to around 5,000 warheads on all missiles on both sides.

Most importantly, however, Reagan then asks that "no more than half of those warheads be land-based." This means roughly 2,500 warheads on land-based missiles. This is crucial because the Soviets have 72 percent of their 7,500 or so warheads on land-based missiles--more than 3,000 of them on the 308 SS18s--while the United States has only 22 percent of its nuclear punch based on land with the rest on submarines and bombers.

Essentially, the administration is trying to force the Soviets away from continuing its emphasis on those threatening land-based systems. The idea is that Moscow would have to pay a very high price, within the overall allowed ceilings, to keep many land-based missiles as opposed to submarine-based missiles. This would also complicate any plans for a surprise attack.

Because submarine missiles are less accurate and therefore less threatening, and also because they are less vulnerable and therefore do not have to be fired quickly, they are generally not viewed as ones putting a hair-trigger on nuclear war. The new U.S. Trident II and Soviet Typhoon missiles now in development, however, will have greater accuracy and thus could also treaten to knock out missile silos.

Aside from warheads, the president has also called for "significant reductions in missiles themselves," which officials privately say means an eventual ceiling of about 850 land- and sea-based missiles for both sides. This obviously will require far greater Soviet than American cutbacks.

These missiles and warhead cuts are meant to be part of what the president called "the first phase" of the strategic arms reductions talks, or START.

Reagan made no public mention of bombers, an area in which the United States has sizable advantages. These weapons, and cruise missiles that fly like jet planes, are also considered less threatening because they take hours to reach their targets and are therefore unlikely to be used in a surprise first strike.

Under questioning, briefing officials said Washington "was prepared to deal with bombers throughout both phases" of the START talks, since Moscow obviously will raise the issue. They said cruise missiles would also be dealt with but declined to say how or when.

Because Russian land-based missiles are so much bigger than their American counterparts, the Soviets also have a roughly 3-to-1 advantage in so-called "throw-weight," meaning the lifting power for hurling either big warheads or lots of them at targets. Therefore, the president said, in the second phase of START he also wants to equalize throw-weight, bringing both sides below current American levels.

Because equalizing throw-weight would mean forcing the biggest possible reductions on Moscow rather than the United States, some Pentagon officials argued strongly that this should be the paramount consideration. State Department officials, with support from the Joint Chiefs of Staff, are said to have argued privately that such an initial focus would make the proposal seem implausible to friend and foe alike.

Yesterday, however, officials stressed that no one's arguments were ignored and that cutting missiles and warheads is one way of cutting throw-weight.

And what about the Russians? The Soviets undoubtedly will reject the initial U.S. offering and argue that the United States seeks to protect its bomber and cruise missile edge and deploy the new MX and Trident while the Soviets are asked to give up the relatively new force of land-based ICBMs that have carried them to such prominence in global power politics. The Soviets will also probably see the proposals as an American effort to push the strategic competition to submarines, where U.S. technology also has an edge.

The administration, to the chagrin of critics, has taken well over a year to come up with this proposal but has made its general views known from the start. Officials said yesterday the plan "won't come as a major surprise" to Moscow and they expect talks to begin late next month.

The Soviets, as viewed from here, have serious economic problems, coming changes in leadership, problems in Poland and elsewhere. This could make talks to try to at least calm down the nuclear threat seem appealing. When asked what the United States would give the Soviets, officials do not mention MX or B1. Rather, they say, "an incentive to reduce the risk of nuclear war."