PRESIDENT REAGAN has accomplished something worthwhile with the Russians, who have spent most of the last four years answering his verbal thrusts and sulking. He has talked them into sending Andrei Gromyko to Geneva in January to start working with George Shultz on an agenda for subsequent arms control talks.

Secretary Shultz's job will be tough. The announcement concerning Geneva was exceptionally ambitious, committing the two governments to "reach agreements" on the "whole range" of nuclear arms. Unless secret consultations produce some progress by then, the secretary and Mr. Gromyko will arrive in Geneva bearing familiar unresolved policy conflicts. The battle over the agenda is always a classic measure-taking exercise. This one, national security adviser Robert McFarlane has said, might require "follow-on meetings."

Is the Soviet Union ready for productive negotiations? The usual political cloud cover over the Kremlin prevents a confident American response. It is worth something, however, that the Soviets felt it necessary to find a way -- by opening these "absolutely new" talks -- to get out of the corner in which they foolishly painted themselves when they walked out of earlier talks to protest Washington's matching of their new missiles in Europe.

Is President Reagan ready? Mr. McFarlane, on Thursday, underlined the president's personal involvement in preparing for the talks and the participation of both Secretary Shultz and Defense Secretary Weinberger. But the degree of Mr. Reagan's engagement and, in particular, the difference between the political points of views represented by the two Cabinet officers stir concern.

It is an encouragement for Mr. Shultz and the like- minded Mr. McFarlane that the drive for talks has been given a positive public launching. The skepticism of Mr. Weinberger and others is nevertheless well known. The one group thinks negotiations can work and can strengthen American security. Doubting it, the other believes that the Soviets can and do exploit the political dynamics to make the United States negotiate with itself to its own disadvantage. Each side in this argument can cite examples from relatively recent history to prove its point. Neither is entirely persuasive nor entirely wrong.

The Geneva talks will demonstrate whether or not this continuing difference within the American government undermines any chance that may arise for reasonable progress. More importantly, the talks will also give a strong clue as to whether the Russians have anything but propaganda and continued stalemate in mind.