London — Britain and West Germany, now both under conservative governments, are setting out to develop a relationship that will enable them to speak with one voice to the Reagan administration.
Already Prime Minister Margaret Thatcher has held two meetings with Chancellor Helmut Kohl - within a month of his taking over in West Germany.
After their first talks in London Mrs. Thatcher spoke of a ''true meeting of minds.'' Then, after talks in Bonn and a tour of the Berlin Wall in Dr. Kohl's company, the British leader spoke of ''a great feeling for cooperation in the future.''
For his part, Chancellor Kohl has helped Mrs. Thatcher unsnarl her quarrel with the European Community over payments into the European budget. West German officials are saying the basis now exists for Bonn-London cooperation over a broad front.
In the past, joint British-German action was made difficult by strains between Mrs. Thatcher and Helmut Schmidt. No such tension exists in the new relationship.
Both Dr. Kohl and Mrs. Thatcher take a robust line on the need to remain militarily strong in the face of the Warsaw Pact, and both are convinced of the need to deploy cruise and Pershing II missiles in NATO countries. This is expected to give them a solid basis in dealings with President Reagan.
At the same time, however, the two leaders have reservations about key aspects of Reagan policy toward Europe. They agree that the President is wrong to continue with sanctions against European firms involved in the Siberian pipeline project.
They also want the Reagan administration to seek openings in negotiations with the Russians on nuclear weapons limitation.
Whitehall sources note that behind Mrs. Thatcher's rhetoric as she gazed at the Berlin Wall, there was a shrewd politician's acceptance of the need to keep channels open to Moscow. Dr. Kohl is also pledged to continue former Chancellor Schmidt's policy of detente with the East.
On this basis, officials in Bonn and London say, the two European leaders hope to be able to influence US policy and make it more flexible on East-West issues.