Mikhail Gorbachev heads back to the Soviet Union today, and the fate of superpower relations passes, for the moment, into the hands of the United States Senate. It is the Senate's task to accept or reject this week's historic arms control treaty, thus determining the immediate path on which US-USSR relations will be placed.
Mr. Gorbachev himself seemed to recognize this when he met with congressional leaders at the Soviet Embassy yesterday. The discussion ranged over the panoply of issues of concern to both countries, including a Gorbachev proposal to establish a dialogue between members of Congress and members of the Soviet parliament about human rights conditions in both countries.
But Gorbachev was particularly eager to press the case for ratification of the accord. ``Congress is indeed the most important element in the political process,'' he said, sitting with top aides across a long, rectangular table from the Democratic and Republican leaders. ``Nothing in this city can happen without its participation.''
Congressional leaders of both parties predict that the Senate will vote to ratify the accord, which would abolish all intermediate-range nuclear weapons in Europe. But the pact has encountered serious opposition from conservatives, some of whom argue that it would leave the US and its allies dangerously vulnerable to the numerical superiority of the nonnuclear military forces controlled by the Soviet-led Warsaw Pact.
Though much of that opposition has softened in recent days, officials in the Reagan administration and in the Soviet government fear that Senate conservatives may succeed in attaching treaty-derailing amendments to the articles of ratification. Dozens of such measures - for example, the linking of the treaty to a redress of the military imbalance in Europe, or a Soviet withdrawal from Afghanistan, or rigorous observance of such earlier US-Soviet treaties as the 1975 Helsinki accord on human rights - are in the works.
As with all treaties, this accord must earn at least a two-thirds favorable vote in the Senate if it is to be ratified. But amendments senators wish to add to the treaty need only win a majority of those present and voting. The disruptive potential of a number of the proposed amendments is enhanced by the fact that many are designed to win broad support in the Senate, even if they are flatly opposed by the Soviets.
``The greatest danger this treaty faces is from the so-called killer amendments,'' says Sen. Alan Cranston (D) of California. ``There will be some very ingenious minds working to try to come up with amendments that don't seem to be killer amendments but are.''
Soviet officials have not tried to conceal their concern about the prospects of passage of those amendments. At the a meeting with congressional leaders Wednesday, Gorbachev seemed to hint that if the Senate attached unacceptable amendments to the treaty, the Soviet government would respond in kind.
House Speaker Jim Wright (D) of Texas related Gorbachev's warning that ``people in the Soviet Union are leery about the symmetry of the treaty'' because it ``calls for the Soviet Union to destroy four times as many missiles.''
Gorbachev also referred to noted similarities between President Reagan's relationship with Congress and his own relationship with the Supreme Soviet, the Soviet Union's nominal parliament. Though the Supreme Soviet has always rubber-stamped the policies of Soviet Communist Party officials, Gorbachev suggested that the treaty signed this week could run into opposition from its members.
``I don't believe everything he said,'' said Senate minority leader Robert Dole (R) of Kansas after emerging from the meeting with Soviet officials. ``I can't believe that the Supreme Soviet acts quite like the US Senate.''
Nevertheless, some lawmakers who attended yesterday's meeting seemed to take Gorbachev at his word when he spoke of his desire for closer US-Soviet relations.
Mr. Wright recalled Gorbachev repeating, ``We have made a decision to move forward in our relationship with the US.'' The Speaker added: ``He was very firm about it.''
Gorbachev's style and words may have impressed many, yet they apparently changed the minds of few. Senator Dole has thrown his support behind the treaty, but only after what he terms a careful evaluation of its contents. Similarly, conservative Sen. Alan Simpson (R) of Wyoming says he intends to support the treaty, because ``the essence is verification, and this [treaty] has verification procedures that are very precise.''
Others remain adamantly opposed. Sen. Larry Pressler (R) of South Dakota calls the treaty ``a potential Trojan Horse,'' in part because it opens the door to more sweeping nuclear arms agreements that could leave the US vulnerable to Soviet conventional military forces. Sen. Malcolm Wallop (R) of Wyoming argues that the treaty's verification procedures are inadequate. Ratification of the treaty as it now stands, he says, ``tells [the Soviets] we're not serious about adherence to arms control treaties.''
Those voices are in a distinct minority now, however. Polls show overwhelming public support for arms control agreements of the type signed this week. Meanwhile, administration officials have been meeting with conservative senators in an effort to craft compromise amendments that would satisfy treaty skeptics and be acceptable to the Soviets.
``We're going to look at the treaty closely,'' says Mr. Dole. ``In the end, it will pass.''