Washington — President Reagan has taken a hard line on the Soviet Union since assuming office. His attitude has generally been approved by the nation.
Now, however, a significant portion of his policy is challenged by the US Chamber of Commerce, which asks why the United States should oppose bringing Siberian natural gas down by pipeline to energy-short Europe. The president of the US Chamber, in a letter to Mr. Reagan, uses such words as ''economic warfare ,'' ''profound change in policy,'' and ''a potentially dangerous conflict'' in NATO.
The chamber's protest has provoked questions within the organization itself. But it appears that the pipeline dispute might bring a national and international reexamination of East-West relations.
The pipeline would bring natural gas 3,000 miles from Siberia to Western Europe. It would cost $10 billion to $20 billion, and would ultimately bring hard currency to the Soviets, helping to finance their East-West trade. The German and French governments are committed to the program, which would free them from dependence on Mideastern oil supplies.
The Reagan administration opposes the pipeline, which it argues would make France and Germany hostage to the USSR. On Dec. 29, Mr. Reagan suspended General Electric's shipment of component compressors, turbine rotors, and pipelaying equipment to Europe.
The US coal industry supports President Reagan. Others oppose the action, as indicated by the Chamber of Commerce.
The division goes into the Reagan Cabinet. Caspar W. Weinberger, the secretary of defense, opposes the pipeline. On the other side, Secretary of State Alexander M. Haig Jr. warns of dangers to the NATO alliance if the US pushes opposition to the pipeline.
Now comes the voice of the Chamber of Commerce. Dr. Richard L. Lesher, president of the chamber since 1975, addressed President Reagan this month in a letter that expresses grave concern at administration policy. The reported policy, he charges, ''would be unprecedented.''
He notes that Western allies view the project as reducing West European dependence on Middle Eastern energy sources, ''a policy actively encouraged by our country until recently.'' It is ''imperative,'' he argues, to help the West Europeans.
Regarding the debate over hard currency earnings by the USSR, Dr. Lesher says this raises an issue which goes to the core of US policy on East-West trade. Such a profound change in policy could be likened to a strategy of economic warfare.
The Chamber's comments represent one of the strongest, though low-keyed, remonstrances that the administration has received from a business group.
America evolved a policy of detente toward the USSR under Presidents Nixon, Ford, and Carter, which was chilled by Mr. Carter after the invasion of Afghanistan and the buildup of Soviet nuclear forces.
At the 1980 GOP convention in Detroit, the platform pledged ''superiority,'' not equality, to Soviet arms. President Reagan has instituted the biggest defense buildup in peacetime history. At the same time, Mr. Reagan ended the Carter embargo on US grain shipments to the USSR, and the US is exporting billions of bushels annually. Why, ask French and German officials, ask us to boycott the Siberian pipeline, when the US is itself profiting from trade with Soviet Union?