Details of British and American strategy for dealing with such sensitive issues as the U.S.-European dispute over the Siberian natural gas pipeline have been disclosed by a small London magazine that said it has more than a hundred pages of classified British government documents.

The documents -- cables and memoranda stamped "secret" or "confidential" -- appear to be material prepared for Foreign Secretary Francis Pym's use at a meeting of European Community foreign ministers last month. Also covered are the Middle East peace negotiations, the community battle with the United States over steel exports, and Britain's efforts to block community aid to the Sandinista government in Nicarargua.

On Friday, after the magazine City Limits appeared, the government obtained an injunction against further use of the documents. But by then they had been made available to other publications, including the London Observer which summarized the contents today. The Foreign Office has not challenged the authenticity of the documents.

None of the material is explosive. But the documents provide a candid look at problems among the Europeans and in Washington over the pipeline impasse, including the attitude of senior U.S. officials involved in the issue.

For instance, the Reagan administration's political dilemma is described in a confidential message from Britain's ambassador in Washington, Oliver Wright, reporting a meeting with Assistant Secretary of State for Economic Affairs Richard McCormack, a former aide to Sen. Jesse Helms (R-N.C.). The cable states:

"He was affable and talkative, and (given his background as a former aide to the right-wing Sen. Helms) encouragingly open-minded about solutions to our current problems.

"He was particularly concerned about the pipeline. He emphasized that no one in the administration wanted our disagreements here to spill over into wider issues and so feed the prejudices of those ordinary Americans who still hanker after withdrawal from entangling alliances.But any settlement would have to meet the president's objective of firm action against the Russians over Poland. And it could not be done by mirrors.

"There were enough expert people (who expressed their views publicly through the Wall Street Journal) who would go through the details of any agreed arrangements for putting economic pressure on the Russians to see whether it matched up with their requirements. It would be politically difficult for the present to back a settlement which could not withstand this critical scrutiny."

The documents show the extent to which hopes for resolving the dispute were riding on a scheduled session last week in New York at which envoys from the four European countries defying President Reagan's ban on equipment for the pipeline were to meet with Secretary of State George P. Shultz. Continuing differences proved so serious that the meeting plan was dropped.

The French had "reluctantly agreed" to the session, according to the documents, and the British were considering "small concessions" to the United States on trade with the Soviets in return for lifting of American sanctions against European companies. However, the document adds, the "French [were] taking hard line, opposed to any European concessions."

Britain's hopes for the New York talks were also reflected in a lengthy message written two weeks ago by Britain's ambassador to NATO, John Graham, concerning the meeting of NATO foreign ministers held in Canada this weekend. Although the session was officially said not to have an agenda, Graham is quoted as listing four items proposed by the Canadian hosts for discussion: consensus on relations with the Soviets; other international issues such as the Middle East; state of the alliance, and the ways to improve alliance consulations.

"All this," Graham adds, "assumes some measure of agreement on the pipeline issue at the meeting in New York... failing progress in New York, the Canada meeting could be very sticky."

City Limits, a generally left-wing weekly publication featuring news and entertainment listings, offers no clues about how it received the material. The Foreign Office was said to be trying to determine where the security breach occurred.