Does the Soviet Union cheat on arms control agreements? Should the United States continue to abide by the SALT II strategic arms agreement? These questions are likely to be the toughest faced by the Reagan administration as it renews its arms control deliberations with Moscow and with the Congress next year.
Determining the seriousness of Soviet treaty hedging and how to balance the risks and benefits of verifying such treaties will have to be settled here before the US can hope to negotiate effectively in Geneva about future arms reductions, administration officials and outside experts agree.
''Issues of verification and compliance have assumed a position center stage with this administration,'' said Robert W. Dean, deputy assistant secretary of state for arms control. ''The administration will accept nothing less than certainty on the monitoring and verification of new treaties, and that issue has not been addressed by the two countries yet.''
In response to a House-Senate request, the White House was to have reported over the weekend on alleged Soviet treaty violations. But the report has been delayed until February, after Secretary of State George Shultz and Soviet Foreign Minister Andrei Gromyko meet in Geneva Jan. 7 and 8.
Some of the 19 allegations involving missile testing and deployment, radar construction, underground explosions, chemical and biological weapons, and other issues are open to considerable interpretation.
Officials say the complexity of the charges has caused the report's delay. But the Reagan administration also does not want to appear to be castigating the Soviet Union just before the restart of arms control talks.
Crossing the verification and compliance hurdles will be anything but easy. In his first presidential press conference, President Reagan accused the Soviet Union of lying and cheating. He has changed the US requirement regarding verification from ''adequate'' (as it was under the three previous Presidents) to ''effective.'' He has refused to seek Senate ratification of two treaties governing nuclear explosions because of verification questions.
The administration must also decide soon whether it will continue complying with the unratified SALT II agreement, which expires at the end of 1985.
Unless the US scraps older submarines, it could exceed SALT II ballistic missile limits when sea trials for the seventh new Trident sub begin sometime next year.
The President has also declared it ''impossible'' to attain comprehensive controls on antisatellite weapons because of verification difficulties.
These days, the White House is stressing flexibility and willingness to negotiate. While it has been under some congressional pressure to do so (as a quid pro quo for keeping the MX missile alive, for example), the administration will also be watched closely by lawmakers on the compliance issue.
Senate failure to ratify SALT II five years ago turned largely on questions of verifiability, and Mr. Dean of the State Department says that oppostion to SALT II ''could be child's play compared with what's to come.''
The political uneasiness about treaty compliance also reflects public wariness over Soviet behavior. A poll taken in October by Daniel Yankelovich for the Public Agenda Foundation showed 82 percent of respondents agreeing that ''the Soviets are dangerous adversaries who are constantly testing us, probing for weakness and quick to take advantage whenever they find any.''
Michael Krepon, an arms control verification expert with the Carnegie Endowment, argues that there are ''all kinds of possible solutions'' to the problem. These include cooperative inspection measures and new ''counting rules'' for such things as cruise missile carriers.
''There's going to be risk with or without arms control,'' Mr. Krepon told a recent round table sponsored by the Scientists' Institute for Public Information. ''The question is, is there going to be more or less uncertainty within an arms control regime?''
But in a report for the Foreign Policy Association, Krepon also notes that ''one branch of (Soviet) military science - maskirovka - is devoted to the arts of deception and concealment,'' and that ''maskirovka programs continue unabated.''
''This is not just a technical issue, but a deeply psychological issue,'' says William Kincade, executive director of the private Arms Control Association. Speaking at the group's annual meeting last week, Mr. Kincade said, ''This will be the most difficult thing the ACA will have to deal with over the next year.''
With the deployment by both sides of such easy-to-conceal systems as cruise missiles (especially those aboard ships and submarines) and mobile land-based ballistic missiles, the problem can only get tougher, especially if the Reagan administration insists on more intrusive verification means such as on-site inspection. Shorter-range tactical nuclear weapons, says John Rhinelander, legal adviser to the SALT I negotiations, ''are far and away the most difficult to verify.''
The Soviet Union has been deploying new battlefield nuclear weapons in Eastern Europe. Such weapons have yet to be addressed in any arms control forum.
In his United Nations speech in September, President Reagan proposed an exchange of US and Soviet experts to measure the yield of each side's nuclear weapons tests. Reagan expressed hope that such an exchange could take place as soon as next spring, and that this would ''enable the two countries to establish the basis for verification for effective limits on underground nuclear testing.''
Soviet leaders have expressed some interest in pursuing such measures. But any comprehensive arms reduction accord of the type sought by the Reagan administration is likely to require stricter verification provisions as well.
''Any potential agreement will require a detailed exchange of information on the nuclear forces of both sides,'' former US Defense Secretary Harold Brown and National War College Prof. Lynn Davis wrote in a paper for the Johns Hopkins Foreign Policy Institute.
''Extensive counting rules and specific definitions will also be needed,'' they wrote. ''Some kinds of limits will also demand rather intrusive inspection measures. Moreover, the United States will need to be satisfied that the Soviet Union has complied with the previous SALT treaties.''