Senior European diplomats today drafted a set of proposals aimed at scaling down the dispute with the United States over the supply of equipment for the Siberian natural gas pipeline, and British officials said the next step is likely to be a similar meeting with Americans.

After a five-hour meeting in London, a British spokesman said that "various proposals were put forward in a spirit of cooperation and solidarity," but he declined to say what they are. Also attending the session were diplomats from West Germany, Italy and France, the other countries challenging President Reagan's ban on the equipment sales.

U.S. officials here and in Washington were closely watching the European discussions. The departure of a Soviet ship scheduled to transport British-made turbines from Glasgow to the Soviet Union was delayed, thus postponing the imposition of sanctions against the British turbine manufacturer, John Brown Ltd. U.S. officials have said no sanctions will be imposed until after the ship sails.

What appears likely to emerge from the talks is a statement by the Europeans that they are taking measures to show firmness in dealing with the Soviets by stiffening credit terms and reducing strategic exports. It is hoped that these measures will go a long way toward satisfying the president's wish for a show of resolve toward Moscow.

Reagan, it is expected, would then lift or further limit the U.S. sanctions on companies defying the ban.

But, sources repeated today, the basic reality of the conflict will not be changed. The four countries will fulfill contracts with the Soviets for the pipeline, despite the president's restrictions on any equipment made with U.S. parts or licenses.

There does, however, appear to have been a change in attitude during the past few days on both sides of the Atlantic. The decision by the administration to limit the punishment of European companies seems to reduce the pain they will feel. For instance, officials at John Brown Engineering Ltd., who were predicting the loss of hundreds of jobs as a result of U.S. penalties, now seem to believe that they will be able to get parts for much of their other work aside from the Soviet contract.

Moreover, the brief visit here by U.S. trade negotiator William Brock has been followed by assertions from spokesmen for the British officials he visited that the talks showed an understanding of a need to find a solution to the crisis. Brock, who is attending a trade conference near Oxford, will be meeting tonight with Britain's minister for trade, Lord Cockfield, who issued the order to British companies to ignore the U.S. pipeline ban.

Last night Foreign Secretary Francis Pym said he hoped a European-American meeting could be arranged for next week.

Showing that alliance relations are not all bad, the Europeans have been making positive remarks about the president's proposals earlier this week for a solution to the issue of Palestinian self-rule. Pym said the plan was "an excellent foundation for negotiations that could lead to a permanent peace in the end."

West German government spokesman Klaus Boelling said the proposals are "emphatically" welcomed as "an important move in the right direction."

The United States had previously been criticized by the Europeans for not being sufficiently tough on Israel after the invasion of Lebanon and failing to stress the need for a Palestinian solution.

[Port workers in Leghorn, Italy, said two turbines destined for the Soviet Union will be loaded aboard a Soviet ship Saturday, The Associated Press reported.]