WHEN President Ronald Reagan of the United States meets Mikhail Gorbachev of the Soviet Union in Geneva in November, they will have before them a long list of subjects on the agenda. Two will be central to what may come of the encounter. Everything else hinges on whether there is a possible meeting of minds on those two. The two essential points at issue are Afghanistan and the nuclear arms race.
I use the word Afghanistan as a shorthand label for the broad issue of attitude by the two superpowers toward each other's clients, dependents, or captives.
It was the Soviet invasion of Afghanistan that wiped out the last remnants of Richard Nixon's ``d'etente.'' And it is Soviet military support for the government of Nicaragua that has made Central America the centerpiece in Mr. Reagan's foreign policy.
The US provides enough military equipment in Afghanistan to keep the rebels in the field. The Soviets do the same for the government of Nicaragua, and rebels in El Salvador.
If ever there is to be a second d'etente, it will have to include a set of rules to regulate or control situations like Afghanistan and Nicaragua.
In this connection, it is to be noted that teams of Soviet and American diplomats met together in Washington on June 18 and 19 to talk about Afghanistan. This was one of the results of the visit to Washington last September of then-Soviet Foreign Minister Andrei Gromyko. Since that September meeting, Soviet and American diplomatic teams have met in Vienna on the Middle East and in Paris on southern Africa.
The meeting in Washington on Afghanistan was intended to supplement and support a series of talks that have been going on at the United Nations in New York aimed at a solution to the Afghan affair. The effort is aimed at an agreement under which Soviet forces would withdraw from Afghanistan, Afghan refugees would return home from Pakistan and Iran, and the outside world would agree to keep out of Afghan affairs.
The other main cause for the breakdown of Mr. Nixon's d'etente was the deployment by the Soviets, beginning in 1975, of 668 supersize SS-18 and SS-19 intercontinental ballistic missiles armed with highly accurate multiple warheads. These weapons could in theory wipe out many, some say most, of the American land-based Minuteman missiles.
It was that deployment which triggered the US search for an answer in the form of the MX and the subsequent deployment in Europe of the Pershing II and Cruise missiles. It was also the impetus for the thinking which emerged in the form of President Reagan's Strategic Defense Initiative (``star wars'').
The Soviets are themselves unhappy about the Strategic Defense Initiative (SDI), because if it works it would neutralize their principal deterrent force. They have put their main effort into these SS18 and SS-19 land-based weapons. If those were neutralized, the Soviets would be in a decidedly inferior ratio to the US since their submarine deterrent is a poor imitation of the superior American Trident submarines.
What trade-offs could there be to reduce the fears each feels about the other's strategic weapons? The US can hardly feel comfortable so long as there is no protection against those 668 huge Soviet ICBM missiles. The Soviets are horrified at the possibility of those being neutralized by Mr. Reagan's SDI.
And by what means might future Afghanistan and Nicaragua situations be avoided or managed? Can Moscow give up giving aid to any ``socialist'' regime without abandoning its ideology? Can the US stand aside and allow Moscow to invade its neighbors without responding as it has in Afghanistan?
If rules could prevent or control future Afghanistans, and if Moscow could cut down its super missiles in return for some limits on SDI, then the Geneva meeting could be the beginning of a new start in US-Soviet relations.
All one can say at the moment is that in various places the working diplomats are doing the preliminary spadework on these problems.