Prime Minister Margaret Thatcher underlined the need for restraint on all sides in the Lithuania crisis during a 50-minute telephone conversation Wednesday with Soviet President Mikhail Gorbachev, her office said. The phone call, arranged in advance through diplomatic contacts, was timed to precede Mrs. Thatcher's meetings Thursday and Friday with West German Chancellor Helmut Kohl in Britain and with President Bush in Bermuda on April 13. Mrs. Thatcher's office gave no details on Gorbachev's response on Lithuania but said she emphasized the need for restraint and negotiations and expressed hope the crisis could be settled in a way suitable to both sides. ``The people of Lithuania have made clear their wish to determine their own future,'' Mrs. Thatcher said to the House of Commons Tuesday. She said Britain had never recognized the 1940 Soviet annexation of Lithuania though it was recognized ``in fact'' in the 35-nation Helsinki accords in 1975. ``Undoubtedly, that is a very difficult situation, both for President Gorbachev and for the people of Lithuania,'' Mrs. Thatcher said. ``I believe that it calls for great restraint on both sides. Force is not an appropriate way to settle the position. I hope it will be settled by restraint on both sides and by their discussing it so that they come to a satisfactory conclusion. ``That view was also taken by the 12 foreign secretaries of the European Community,'' she said. Mrs. Thatcher's spokesman, who by custom was not identified, said the conversation also covered other world events, including the East German elections, prospects for German unification, and the prime minister's visit to Kiev in June.