Soviet Foreign Minister Eduard A. Shevardnadze will meet in Washington with Secretary of State James A. Baker from April 4-6, the State Department announced Friday. The talks are designed to further preparations for the summit meeting President Bush will hold here with Soviet President Mikhail S. Gorbachev sometime in June. Shevardnadze and Baker are expected to concentrate on arms control issues, hoping that a treaty to reduce U.S. and Soviet long-range nuclear missiles would be ready for signing at the summit. They will also discuss regional issues and human rights, among other subjects, Margaret D. Tutwiler, the State Department spokeswoman, said.