President Reagan's meeting with West German Chancellor Helmut Schmidt is an attempt to prevent the differences between West Germany and the United States over Poland from widening.
In a two-day series of conferences here between Mr. Reagan, members of his Cabinet, and Mr. Schmidt, officials will do their best to minimize differences between the two countries over how to respond to the Polish crisis.
On the other hand, observers agree that it is a testing time for the NATO alliance. They add that a new relationship may be necessary between Washington, which already has applied sanctions against Moscow, and the West Germans, who want the US to tone down its rhetoric toward Moscow and who want to proceed with the pipeline deal to bring natural gas from Siberia into Europe.
So far, the US has been alone in imposing sanctions. Some observers feel that closer coordination among the NATO allies is necessary to present a united front. The alternative is a possible split in the alliance. Schmidt's visit is the first part of an attempt at coordination. On Jan. 11, the foreign ministers of the 15 NATO countries meet in Brussels to discuss further actions. The US will be represented by Secretary of State Alexander M. Haig Jr., and a free-wheeling discussion is likely -- focussing on repression in Poland, the response of the Western countries, and their future policies.
In a briefing here a State Department official noted that Moscow has taken a notably harsher line toward the United States than toward West Germany. It is not the purpose of the Reagan-Schmidt talks to reach final agreement, it is said , but to exchange views on the reaction of the West. The US hopes for parallel action from allies and, in any event, action that does not undercut the American course.
The US has three objectives, according to the official: to get martial law lifted; to get the detainees released; and to see negotiations resumed between the Polish government and Solidarity, the workers' union. The Soviet Union's tone to the US, it is noted, is ''extremely negative'' -- not to say harsh, whereas that to the West Germans is noticeably softer.
Officials make plain that Reagan and Secretary of State Haig are not pressuring Schmidt but exploring his viewpoint. They acknowledge there is an essential area of disagreement: Americans oppose the pipeline deal, but they say it is not a disagreement that can't be resolved. They want to find out, too, the meaning of the softer line the Soviets have taken with Bonn as compared with Washington.
The meetings between Reagan and Schmidt come at a time when the President is considering a change in national security advisers and preparing for a showdown with Congress over a budget deficit that by some estimates may surpass $100 billion.
A longtime Reagan associate, Deputy Secretary of State William Clark, is in line to replace national security adviser Richard V. Allen. Reagan is putting the final touches on his budget message to Congress. And in Peking, China has delivered the strongest warning yet that it won't hesitate to sacrifice relations with the US if Reagan sells arms to Taiwan.