Geneva seen as solid gain, especially for U.S. Question remains: Can both superpowers overcome past antagonism to reach accord?

Now comes the hard part. The United States and the Soviet Union have agreed to resume talks about nuclear disarmament and have added the new issue of space weapons to the coming negotiations.

But following a year of especially frosty relations, in which no arms control discussions were held, a key question remains: Will the antagonism and mistrust -- the inclination of both sides over the last five years to seek military and political advantage -- be overcome in a true search for greater stability?

Arms control advocates remain skeptical that a comprehensive agreement limiting nuclear and space weapons can be achieved, given recent past history. But they say they are encouraged that talks are resuming, and they laud the new format, in which offensive and defensive systems will be negotiated in close parallel.

``I think it's the only way to conduct these talks, because indeed the issues are interrelated, not just technically but politically,'' says William Kincade, a senior associate and arms control expert with the Carnegie Endowment for International Peace. ``But having said that, there's no way that an elegant forum will substitute for political will or consensus on negotiating strategy.''

Other high-level observers are moderately upbeat as well.

``It's a substantial success, because we got the Soviets back to the arms control discussions,'' says former Secretary of State Alexander M. Haig Jr. ``And we've done so without preconditions on either side, which is an encouraging success.'' Mr. Haig has been sharply critical of administration arms control efforts during President Reagan's first term.

Talk of who would head the new US negotiating team centers on Washington lawyer Max Kampelman, whose most recent government service has been as chief of the US delegation to the 35-nation Conference on Security and Cooperation in Europe. These are follow-up discussions to the 1975 Helsinki agreement on human rights and security issues in Europe. Here, Ambassador Kampelman gained considerable experience in tough, behind-the-scenes talks with Soviet officials.

Like UN Ambassador Jeane J. Kirkpatrick and arms negotiator Paul H. Nitze, Mr. Kampelman is a conservative Democrat and one of many Reagan administration officials, past and present, associated with the relatively hawkish Committee on the Present Danger.

Yet Kampelman is amiable and smooth in his personal relations and also is less ideological than many of those associated with the conservative private group. At this writing, he would not confirm or deny his appointment, which was first reported by CBS News. State Department and other government officials said such things were yet to be decided.

One of the toughest jobs for Secretary of State George P. Shultz and other arms control overseers will be to maintain control of the various factions in the administration who have different and in some ways conflicting personal agendas for arms control, especially how and when to bargain over the President's Strategic Defense Initiative, or ``star wars.''

It appears that the US and the Soviet Union had to give up something at Geneva this week.

Moscow backed away from its insistence that US-built missiles be removed from Europe before talks on medium-range missiles resume; and it did not obtain a moratorium on antisatellite weapons tests as a condition to talks on the arms race in space. The US agreed to give equal prominence to advanced space-based strategic defenses, which remain a key goal of President Reagan. The Americans will find it most difficult to explain what they see as a new relationship between offensive and defensive systems, a notion already criticized by many US experts and Western European leaders, as well as the Soviet Union.

Both sides will have to reexamine their positions on strategic arms reduction and talks on intermediate-range nuclear forces -- positions that had been adjusted several times in recent years.

Initial congressional reaction to Mr. Shultz's mission is positive. The Senate Foreign Relations Committee chairman, Sen. Richard Lugar (R) of Indiana, called it an ``extraordinary diplomatic success.'' Sen. Lloyd Bentsen (D) of Texas said the new arms control talks would have ``substantial bipartisan support.''

This week's outcome also is likely to bolster Reagan's case for continued funding for the MX missile, testing of antisatellite weapons, and strategic defense research, which all face sharp opposition in Congress. But administration officials assert that the US arms buildup brought the Soviets back to the table. -- 30 --{et