One early stumbling block U.S. and Soviet representatives may face in the new round of arms-control talks scheduled next week in Geneva is the difficult question of "interim restraints" on the two countries' space programs as proof of good faith as a long negotiating process begins.

The sharply divergent views apparent in Washington and Moscow on this issue illustrate the enormous gap separating the two nuclear superpowers on preliminary as well as underlying questions of offensive and defensive weapons.

Moreover, the series of compromises by which the Reagan administration is formulating its position on interim restraints reflects the bureaucratic infighting that must be overcome to reach a negotiating position to present to the Soviets.

Administration sources said last week that there is full agreement in the executive branch on the initial U.S. position to be taken to Geneva by Secretary of State George P. Shultz.

This position is to refuse to work out any such self-denying steps until full-scale negotiations begin between the two nuclear superpowers.

President Reagan has yet to decide what to offer or accept if the negotiations do get under way.

His administration has been sharply divided since last summer on whether to offer some form of temporary halt to the testing of U.S. antisatellite weapons.

The Soviet Union, in proposing talks on the demilitarization of space last June 29, called for a moratorium on the testing and deployment of all space weapons to take effect as the two powers sat down to bargain.

The bargaining session had been scheduled to take place in Vienna Sept. 18 but no meeting was held because of differences between the countries, exacerbated in a crossfire of sharp rhetoric.

One of the central differences that killed the proposed Vienna talks was the U.S. insistence on discussing limits on offensive nuclear weapons there, in addition to space weapons as the Soviets desired.

More than a year ago the Soviets broke off negotiations on long-range, or strategic, and intermediate-range offensive nuclear forces.

Last month the two powers agreed that the newly scheduled Jan. 7-8 meeting in Geneva will cover offensive as well as defensive systems.

This means that the Soviets implicitly have backed off their earlier position on this point.

The other main barrier to the Vienna meeting was U.S. refusal to accept the Soviet-proposed moratorium on testing and deployment of space weapons, which was to include antisatellite weapons as well as antimissile weapons in space.

Antisatellite weapons attack the satellites whirling over the globe which the United States and the Soviet Union rely upon for global communications, control of military weaponry and surveillance.

Antimissile weapons, such as those envisaged in Reagan's "Star Wars" Strategic Defense Initiative, would attack the other nation's offensive nuclear missiles or warheads as they travel through space to their targets across the globe.

In U.S. deliberations on the Soviet offer, the State Department proposed exploring a three-year moratorium on testing U.S. antisatellite weapons as part of tradeoffs with the Soviets that would also involve offensive nuclear forces. According to administration sources, the State Department, backed by some elements of the military, argued that reconnaissance and communications satellites are more vital to American security than they are to the Soviet Union, and that it is in U.S. interest to retard any competition to develop effective satellite killers.

The State Department also was ready to explore a five-year moratorium on testing antimissile weapons in space as contemplated in Reagan's initiative. Department officials reportedly argued that the pace of research would not call for such tests during the next five years anyway, so nothing would be given away.

The Defense Department strongly opposed both of these proposed restraints on U.S. programs. Pentagon officials argued that the Soviets already have deployed a low-altitude antisatellite weapon, and that the United States should match it before any agreement to limit U.S. development.

They also strongly resisted any deals with the Soviets that could affect Star Wars, contending that it would be difficult to abandon even a "temporary" moratorium once the two superpowers agreed to implement it.

Reagan never chose last summer between the contending positions and, so far as could be learned, still has not. The State Department is reported to have recently amended its plan for a three-year ban on antisatellite testing to permit the United States three or four tests that would give a new U.S. weapon a limited operational capacity roughly parallel to the Soviets'. The department is said to have backed off the space weapons test ban, in deference to the strong support for Star Wars.

The Defense Department appears to have hardened its resistance to temporary restraints of any kind, arguing that historically they have tended to strengthen the Soviet bargaining positions and work against U.S. interests.

One point on which the contending forces were able to agree last summer, and which unites them now, is that the United States should accept no such "interim restraints" in the period of talks and jockeying before negotiations begin.

This agreement was enshrined in the slogan that it would be wrong to "reward the Soviets for returning to the bargaining table."

Soviet Foreign Minister Andrei A. Gromyko is expected to press Shultz at Geneva on the space moratorium issues. It is not known how hard he will push this.

In agreeing to the Geneva talks without advance agreement on any moratorium, Gromyko in effect has eased off one notch from Moscow's previous position.

Some hints from the Soviet side suggest that Moscow will be willing to go further by agreeing to begin full-scale negotiations on space weapons without advance agreement on "interim restraints." The understanding would be that this issue would be an early order of business when the negotiators get down to bargaining.

The basic Soviet position is that an extension of the arms race into space should be stopped by sweeping prohibitions. In a letter Sept. 28 to United Nations Secretary General Javier Perez de Cuellar, Gromyko declared, "Space weapons of any basing mode should not be developed, tested or deployed either for antiballistic missile defenses, or as antisatellite systems, or for use against targets on the earth or in the air. Any such systems already created should be destroyed . . . . The U.S.S.R. proposes that agreement be reached on a radical solution to the question of preventing the militarization of space -- on banning and eliminating space attack weapons, as well as any ground-, air- or sea-launched systems designed to destroy objects in outer space."

The Reagan administration, on the other hand, looks to antimissile developments in space with hopes for advancing U.S. security and breaking out of the postwar reliance on "mutual assured destruction" -- restraint through the threat of retaliation -- as the basis for the relations between the nuclear superpowers.

Moreover, the United States always has opposed broad bans on weapons developments, partly on grounds they would be difficult to verify. Reagan's position on partial and temporary restrictions on military uses of space is at the heart of the bargaining both within the administration and between the United States and the Soviet Union.