Three weeks before the Geneva summit meeting between President Reagan and Soviet leader Mikhail Gorbachev, the superpowers appear surprisingly close in their views on what a nuclear arms cut should accomplish but fundamentally at odds over how to deal with weapons in space.

For the first time in nearly five years since the Reagan administration took power, according to a U.S. diplomat close to the Geneva talks, "the dynamics are there for real negotiations."

As the third round of Geneva arms talks closes Friday and the spotlight shifts to the summit, both sides have presented comprehensive arms-control proposals which, for the first time in this decade, have outlined the thinking in Moscow and in Washington on how to deal with the three basic issues -- strategic nuclear weapons, intermediate-range nuclear forces (INF) and space weapons.

Neither superpower expects a substantive weapons pact to emerge from the Nov. 19-20 meeting. However, Secretary of State George P. Shultz has been invited to Moscow next week to meet Gorbachev in hopes of drafting a timetable which could be unveiled at the summit as a mutual scheme to expedite work toward an agreement.

The most-promising area appears to be in talks on European-based intermediate-range missiles because of a recent Soviet proposal to freeze these weapons at current levels. As to intercontinental ("strategic") weapons, both sides favor halving arsenals but disagree over which weapons would be cut and how the surviving forces would be limited.

And in space weaponry, although Moscow and Washington appear to have moved closer on what can be tested under the 1972 Antiballistic Missile Treaty, they disagree on whether to permit weapons in space.

After three rounds of arms talks spanning eight months, here is where the two sides stand: Strategic Weapons

Cutting both superpowers' arsenals in half was first suggested years ago by former U.S. ambassador to Moscow George Kennan. It resurfaced as the central element in the new Soviet proposal delivered to Reagan last month.

A senior White House official recently told journalists that "we have for a long time proposed a reduction of about half in land- and sea-based ballistic missiles." That was later said to refer to the administration's 1981 proposal for strategic arms reductions.

On the question of what to cut, the Soviets want to include not only strategic intercontinental ballistic missiles (ICBMs) and long-range bombers, but also U.S. medium-range Pershing II and ground-launched cruise missiles based in Europe, as well as shorter-range bombers based in Europe and on carriers that are capable of dropping nuclear weapons on the Soviet Union.

The United States strongly disputes inclusion of the European systems. If the U.S. definition of delivery vehicles is accepted, the two sides are relatively close: 2,504 for the Soviets, 2,210 for the United States.

Many U.S. officials believe the Soviets might agree to exclude the U.S. European systems from the strategic package if Moscow's recent offer is accepted for an interim freeze on intermediate-range missiles, which would include the Pershing and cruise missiles. A Soviet official said that under such an agreement the problematic issue of European weapons "would be swept aside."

The two sides also agree they should have equivalent numbers of nuclear weapons after the launcher reductions. The Soviets, however, want to count as equals fast-flying ballistic missile warheads as well as slower-moving, air-launched cruise missiles and nuclear bombs carried by aircraft.

The United States argues that missile warheads which can hit targets in 30 minutes after being launched are more dangerous and should be counted in one category. The bomber-carried cruise missiles should count in another category and bombs should not count at all, the U.S. argues.

Since the Soviets proposed counting all nuclear weapons equally, Pentagon officials have developed the rationale that nuclear bombs and short-range nuclear missiles carried by bombers should not be counted, since they are carried to help U.S. bombers overcome Soviet air defenses.

Although U.S. negotiators have told the Soviets in earlier negotiations they would be willing to work out a way to count U.S. bomber-carried weapons, that has never been done, according to U.S. officials.

One administration arms-control expert said last week that the Soviet proposal has forced the Pentagon for the first time to ponder how valuable the new B1B and Stealth strategic bombers will be to U.S. strategic nuclear plans, since bombs and cruise missiles carried by bombers will ultimately have to be counted against any overall limit on them and on intercontinental missiles in a future arms control agreement. In other words, the United States may ultimately have to give up more potent missiles in order to keep these bombers in the force.

Both sides also agree that there should be a "sublimit" on the weapons allowed after a 50 percent reduction in order to guarantee that neither side has the ability to launch a surprise first-strike attack against the other side's strategic nuclear forces. They do not agree, however, on how sublimits should be measured.

The Soviets want to cap the number of warheads that can be on any one of the three types of delivery systems (ICBMs, bombers and submarine-launched missiles). The United States wants to limit warheads and also the carrying capacity of each missile, known in nuclear jargon as throw weight. The United States believes such limits would prevent first-strike capabilities now and forestall either side from developing such a capability in the future by adding more warheads on missiles after an agreement is signed.

U.S. and Soviet missile warhead totals currently are about equal at roughly 8,000 for the United States and 9,000 for the Soviet Union. Less equal, however, is the lifting capacity or throw-weight totals, in which the Soviets, who have traditionally built larger missiles, hold nearly a 3-to-1 advantage.

On the other hand, the U.S. advantage in air-launched cruise missiles is also about 3 to 1.

One important subject of disagreement is the building of future strategic weapons. The Soviets want to permit modernization of current systems while limiting deployment of new systems. The United States wants each side free to build new systems as long as they stay within the agreed limitations.

Other unresolved issues include the handling of U.S. Pershing and cruise missiles and a mutually acceptable way to limit the intercontinental forces that would still be permissible, notably the 308 giant Soviet SS18 missiles that the United States has long sought to cut because of their potential as first-strike weapons.

The Soviets also want any accord on strategic forces to be contingent on mutual agreement to ban what Moscow calls "space-strike weapons." The United States argues that agreement in any one area should not be dependent on accord in any other area. Space and Defense Weapons

Moscow wants to ban development, testing and deployment of space-strike weapons, a phrase intended to cover not only the president's Strategic Defense Initiative (SDI), but also the development of U.S. antisatellite weapons.

The Soviets have indicated, however, that they are prepared to permit U.S. research testing in space of sensors and other devices that could be associated either with modernizing traditional ground-based antiballistic missile (ABM) systems, or with SDI's futuristic weapons.

But the Soviets would not allow tests of space-based weapons or "models, pilot samples, separate assemblies and components," as Marshal Sergei Akhromeyev recently put it, of missile-killing lasers, particle beams or hypervelocity guns that also could be part of the "Star Wars" program.

The United States, for its part, is determined to proceed with Star Wars research and development to determine whether the president's dream of a space-based missile defense is practical. The tests in space now planned by the Pentagon over the next five years will not use models of SDI weapons, but rather components to determine if weapons can be built eventually along with the associated warning and guidance sensors critical to missile defense.

U.S. negotiators in Geneva, however, have not offered any proposals on how to accommodate the U.S. view on space weapons.

American negotiators instead have described to the Soviets how SDI research and testing over the next few years would stay within the limits of the ABM Treaty, according to U.S. officials. They have also said that it take three to five years, according to one source, before SDI research indicates what modifications, if any, would be needed in the treaty to permit Star Wars to continue.

Under pressure from the Soviets to make a space proposal, U.S. officials have have been searching for a position that would not interfere with SDI research. According to some U.S. sources, Washington is prepared to guarantee Moscow that the United States would negotiate the introduction of any new defensive system while also extending the current six-month warning period now required for treaty abrogation to as long as seven years.

White House spokesman Larry Speakes, along with State and Defense department officials, has denied that such proposals are being pondered.

Although the Soviets want to ban development of space weapons, they appear to recognize that both sides will conduct tests in space of devices with ABM capabilities in the future. Having backed away from their initial position of barring all research, Moscow seems to be searching for ways to isolate U.S. testing of space-based weapons.

The most detailed presentation from Moscow on possible compromises on the space issue came recently from Akhromeyev in an interview in Pravda, the Communist Party daily, considered so important by the Soviets that they translated it and reprinted it in a full-age ad in last Friday's Washington Post.

Akhromeyev argued that the Soviet position "does not deny the right and possibility of conducting basic research in outer space." He added, however, that the Soviets view as "impermissible" development and testing of models.

He also stressed that determining a test of an impermissible "space-strike weapon" could be verified by "national technical means" -- the arms-control phrase meaning electronic intelligence systems including spy satellites maintained by each country.

In a slight, but significant, change of wording, the Soviet chief of staff said that everything being done for the "subsequent design and production of space-strike systems" -- not just space-strike weapons themselves -- "should be banned." By using the verb form "should," Akhromeyev implied that those steps are not prohibited by the treaty.

In short, the Soviets want to ban SDI, but recognize that research programs including tests are permissible up to a certain point without modification of the ABM Treaty. Whether the two sides can agree on where that threshold lies remains to be seen.

Finally, Soviet officials have said they want some general statement of U.S. intent on space-weapon issues. They recognize that Reagan will no longer be in the White House if and when the United States decides to build a defensive system. But as one top Soviet scientist said recently in Moscow, "We don't want to wake up one morning and find the U.S. ready to begin deploying within a year. "Intermediate-Range Nuclear Forces

New Soviet proposals have transformed the talks on European-based, intermediate-range forces (INF) from the least to perhaps the most-promising area for Soviet-U.S. agreement. The Soviets have apparently decided that the time has come to cut the diplomatic losses piling up ever since they began opposing deployment of new U.S. missiles in Europe.

In Geneva, the Soviets recently proposed an interim freeze on deployment of new U.S. missiles in Western Europe in exchange for a freeze on Soviet SS20 missiles in the Far East and reduction of their European SS20s to 243 missiles. Under the Soviet offer, both sides would later readjust missile numbers with the Soviets allowed compensation for British and French nuclear forces. Similar proposals to compensate the Soviets for British and French weapons have been rejected by the NATO allies.

Nevertheless, as one U.S. official noted last week, once the interim freeze agreement took effect, there would be no pressure to take the second step toward reductions.

There are snags in the Soviet offer from a U.S. perspective. The main one is the question of whether the proposed freeze, which would allow the United States to keep all its presently deployed Pershing and ground-launched cruise missiles, will mean that those systems would no longer be considered part of the strategic weapons arsenal.

A hint that the Soviets have worked all this out is contained in the written answers Akhromeyev supplied to The New York Times on Oct. 12, more than a week after the Soviet arms proposal was presented at Geneva.

The Soviet chief of staff, in listing the superpower nuclear balance, excluded the Pershing and cruise missiles from the U.S. strategic force. Instead, they were listed within the "medium-range nuclear weapons" category and counterbalanced the Soviet SS20 missiles.

Akhromeyev also presented a new formulation of the INF balance.

"The U.S. has already deployed 209 missiles in Western Europe," he said, a total that Soviet officials said included 81 Pershing missiles. Akhromeyev added, "The whole NATO block has in Europe 387 medium-range missiles capable of carrying 739 warheads."

He went on to list the Soviet European SS20s at 243 missiles.

He failed to mention that the SS20s, each of which carries three warheads, would give the Soviets 729 warheads in Europe, a total roughly comparable to the combined warheads of the U.S., British and French forces.

In his more recent Pravda statement, Akhromeyev said the ultimate Soviet goal is to have equal amounts of warheads in Europe for the Soviets and the combined British and French forces.

But as the numbers show, that goal can be met by the current freeze proposal if U.S. missile warheads are included.