The chief US negotiator in talks on medium-range nuclear missiles says he is returning to Geneva prepared to renew his pursuit of President Reagan's original ''zero option'' proposal.
Paul H. Nitze, head of the American delegation to the talks, which began more than a year ago, also says that he is optimistic about the outcome of the next round of negotiations, which opens Feb. 27.
''The basic position continues to be that zero-zero would be the best outcome if one can get it,'' said Ambassador Nitze in an interview with the Monitor. That proposal, put forth in a speech by President Reagan on Nov. 18, 1981, calls for the elimination of more than 600 Soviet missiles carrying some 1,300 warheads capable of striking Western Europe. In return, the United States would agree not to deploy the 572 new single-warhead missiles it now plans to place in Western Europe over the next few years.
But he added that ''now the question is whether there is some other outcome which is worthy of serious consideration.'' This seemed to indicate that there was some flexibility in the US position.
''The President made it clear right from the beginning of these negotiations that if these were to be serious negotiations, we would give careful consideration to any responsible idea which the Soviets might advance,'' said Nitze.
The US negotiator also said, ''I'm going into these negotiations -this next round - with a feeling of optimism. You can't deal with a negotiation of this kind constructively unless you approach it from an optimistic standpoint.''
Last July, Ambassador Nitze and his Soviet counterpart, Yuli A. Kvitsinsky, developed what Mr. Nitze calls an ''exploratory package of ideas'' that would have marked a departure from the original Reagan zero option proposal.
Under the Nitze-Kvitsinsky package, the two sides would have stopped short of this. Each side would have been permitted 75 missile launchers. Nitze said that although Ambassador Kvitsinsky helped to develop the package, the Soviet government ended up rejecting it. The US government, Nitze said, ''found some things in it which we preferred to do a little differently.''
This negative outcome led some observers to the conclusion that Nitze's negotiating authority had been diminished and that he might resign. But Nitze gives every indication that this is not the case, and that any new ideas put forth by the Soviets would be carefully considered.
Despite Nitze's professed optimism, some administration officials are convinced that the Soviets' overriding aim at this point is not an arms control agreement but the splitting of the Western alliance. Others are convinced that nothing will happen in the arms control negotiations until the two sides can assess the outcome of West Germany's elections, scheduled for March 6.
On Jan. 18, in the course of a visit to West Germany, Soviet Foreign Minister Andrei Gromyko rejected the Reagan administration's zero-option proposal and blamed Washington for a lack of progress in the arms control talks. Gromyko denied reports that Ambassadors Nitze and Kvitsinsky had reached an informal understanding which fell short of the zero option.
Mr. Kvitsinsky has a reputation in Washington for being an imaginative negotiator. To back this up, an official pointed to his role in helping bring about an agreement on Berlin in the early 1970s. But Kvitsinsky was reported to have been reprimanded for going too far in his informal talks with Nitze.
In the Monitor interview, Nitze said that what the Soviets have formally proposed to the US was totally unacceptable. He said that it would permit the Soviets to maintain 162 SS-20 missiles in European Russia without imposing any constraint on SS-20s outside that area. The US, on the other hand, would be unable to deploy any of the planned 572 Pershing II and ground-launched cruise missiles and would also face constraints on American aircraft based in Europe which are capable of carrying nuclear bombs.
Nitze said that the Soviet proposal as put forth by the Soviet leader, Yuri Andropov, was ''wholly one-sided.''
The ambassador declined to comment on reports that the administration had failed to resolve differences between the State and Defense Departments over arms control. According to these reports, civilian officials at the Defense Department tend to be skeptical of the idea any kind of arms control agreement with the Soviets and are firmly opposed to any retreat from the zero-option proposal.